1,2-Addition (Sec 13.10, 19.7): An addition reaction in which two groups add to adjacent atoms in a conjugated system, which is fast and under kinetic control; in α,β-unsaturated carbonyl compounds, a nucleophile adds to the carbonyl carbon and the carbonyl oxygen is protonated. Also called simple addition.

1,2-Dihydroxylation (Sec 8.16, 11.15): Reaction that coverts an alkene into a vicinal diol (glycol).

1,2-Elimination (Sec 6.15, Lab 10.1): An elimination reaction that results in the loss of two groups from adjacent atoms on the substrate, with the formation of a pi bond. Also called β-elimination.

1,2-Shift (Sec 7.8A): A rearrangement that occurs when a less stable secondary carbocation rearranges to a more stable tertiary carbocation, through the migration of a hydride, methanide, or alkanide anion from a carbon adjacent to the carbocation.

1,3-Diaxial interaction (Sec 4.12): Repulsive forces produced by steric strain between groups in axial positions on the same side of a cyclohexane ring.

1,3-Dithiane derivative (Sec 19.7): A class of six-membered ring thioacetals produced by the reaction of an aldehyde with 1,3-propanedithiol; the hydrogen atom on the carbon between the sulfur atoms is acidic with a pK_a of 32; it can be deprotonated into a carbanion by reaction with an alkyl lithium compound.

1,4-Addition (Sec 13.10, 19.7): An addition reaction in which two groups add to atoms that bear a 1,4-relationship in a conjugated system, which is energetically favored and under thermodynamic control; in α,β-unsaturated carbonyl compounds, a nucleophile adds to the β carbon and the carbonyl oxygen is protonated. Also called conjugate addition.

2,4-DNP derivative (Sec 16.8B, Lab 25.7A): A hydrazone formed by the reaction of an aldehyde or ketone with 2,4-dinitrophenylhydrazine.

α Carbon (Sec 18.1): The carbon atom adjacent to a carbonyl group.

α Hydrogen (Sec 18.1, 18.5): The hydrogen atom on an α carbon; this H is unusually acidic, with a pK_a between 17 and 20 for most monocarbonyl compounds, or a pK_a between 9 and 11 for most β-dicarbonyl compounds. Also called α proton.

α Selenation: A reaction in which a lithium enolate is selenated with benzeneselenyl bromide, then the α-selenyl ketone is converted to the α,β-unsaturated carbonyl by reaction with hydrogen peroxide.

α Substitution (Sec 17.3, 18.4): Replacement of a hydrogen atom on the α carbon atom of a carbonyl compound by some other group.

β-Dicarbonyl (Sec 18.2, 19.1): Compounds that have two carbonyl groups, >C=O, that are separated by one carbon atom, with the general formula, RCOCH₂COR.

β Diketone (Sec 19.1): Compound of the type RCOCH₂COR. Also called a 1,3-diketone.

β Elimination (Sec 6.15, Lab 10.1): A reaction that results in the loss of two groups from adjacent atoms on the substrate, with the formation of a pi bond. Also called 1,2 elimination.

δ+ : The region in a molecule or ion that has low electron density and a partial positive charge.

δ─ : The region in a molecule or ion that has high electron density and a partial negative charge.

σ (sigma) bond (Sec 1.12): A connection between two atoms in which the orbitals involved overlap along the internuclear axis. A cross section perpendicular to the internuclear axis is a circle.

π (pi) bond (Sec 1.13): In alkenes, a bond formed by overlap of p orbitals in a side-by-side manner. A pi bond is weaker than a sigma bond. The carbon-carbon double bond in alkenes consists of two sp²-hybridized carbons joined by a σ bond and a π bond.

π → π^* Transition (Sec 13.9): Excitation of a π electron in a HOMO bonding π orbital to a LUMO antibonding π^* orbital by ultraviolet or visible light.

n → π^* Transition (Sec 13.9): Excitation of an electron in a lone-pair nonbonding n orbital to a LUMO antibonding π^* orbital by ultraviolet or visible light.

A

Abscissa: The horizontal axis in a set of two-dimensional coordinates; commonly referred to as the X-axis.

Absolute configuration (Sec 5.l5A): The three-dimensional arrangement of atoms or groups at a chirality center.

Absolute ratio of integrated peaks (Sec 9.3, Lab 8.3): In ¹H NMR, the ratio that the sum of the integers in the relative ratio of integrated peaks gives the actual number of hydrogens present in the molecule.

Absorbance, A (Sec l3.9, Lab 8.4): A measure of the amount of light absorbed by a substance, according to the formula: A = log(I₀ / I) = log(100 / %T), where I₀ is the intensity of light entering the sample at a particular wavelength, and I is the intensity of light exiting the sample at the same wavelength. The larger the value of A, the greater the amount of radiation that is absorbed by the sample. Also called optical density.

Absorption (Sec l3.8, Lab 5.3, 8.4): (1) The process by which a substance enters the volume of another substance, often to form a solution. (2) The uptake of energy from radiation by the medium through which it passes.

Absorption maximum, λ_max (Sec l3.8, Lab 8.4): The wavelength at which the absorption is at a maximum. Also called absorbance peak.

Absorption spectroscopy (Sec l3.8, Lab 8.4): The measurement of the amount of light absorbed by a compound as a function of the wavelength.

Absorption spectrum (Sec l3.8, Lab 8.4): A plot of the wavelength of a region of the spectrum versus the absorbance at each wavelength.

Acetal (Sec l6.7B): The product of the nucleophilic addition of two molecules of an alcohol to an aldehyde or ketone, with loss of one molecule of water; the acetal has two alkoxy groups, -OR, on the former carbonyl carbon atom. This derivative of a ketone is also called a ketal.

Acetoacetic ester synthesis (Sec 18.6): Base-catalyzed alkylation or arylation of the enolate of a β-ketoester to produce a monoalkyl or dialkyl acetoacetic ester; subsequent hydrolysis of the ester and decarboxylation produces a monosubstituted or disubstituted acetone (methyl ketone).

Acetyl group (Sec 16.2): The -COCH₃ group. Also called an ethanoyl group.

Acetylene (Sec 1.14, 7.1, 7.11): A common name for ethyne, HC≡CH. Also used as a general name for alkynes.

Acetylenic hydrogen atom (Sec 4.6, 7.9): The hydrogen atom that is bound to a carbon atom of a

terminal alkyne, H-C≡C-R .

Achiral molecule (Sec 5.3): A molecule that is superposable on its mirror image, that lacks handedness, and no enantiomer of the molecule can exist.

Acid (Sec 3.2, 3.3): An Arrhenius acid is a compound that dissociates in water and releases hydrogen ions; a Brønsted-Lowry acid is a proton donor; a Lewis acid is an electron-pair acceptor.

Acid anhydride (Sec 18.2F, 18.6): An activated carboxylic acid derivative formed from two acid molecules with loss of a molecule of water; a mixed anhydride is derived from two different carboxylic acid molecules. Also called carboxylic acid anhydride, or carboxylic anhydride.

Acid-catalyzed hydration of alkenes (Sec 8.5 - 8.10, 11.4): The Markovnikov addition of the components of water, H-OH, to the C=C group of an alkene, which forms an alcohol; the acid catalyst adds H⁺ to form the more stable carbocation (which may undergo rearrangements), then water adds to the carbocation; after deprotonation, the more substituted alcohol is the product as a mixture of syn and anti addition products.

Acid-catalyzed ring opening of an epoxide (Sec 11.14): In acidic solution, a nucleophile attacks an unsymmetrical epoxide primarily at the more substituted carbon of the epoxide by an S_N1 like mechanism.

Acid chloride (Sec 15.7, 18.2G, 18.5): An activated carboxylic acid derivative in which the hydroxyl group of the acid is replaced by a chlorine atom, RCOCl. Also called acyl chloride.

Acid dissociation constant, Ka (Sec 3.5): The equilibrium constant for the reaction: HA ↔ H ⁺ + A^‾ is defined as: Ka = [H ⁺ ][A^‾ ] / [HA] and pKa = -log Ka. Also called acidity constant.

Acid halide (Sec 18.2G): A general name for activated carboxylic acid derivatives in which the hydroxyl group of the acid is replaced by a halogen atom, RCOX. Also called acyl halide.

Acid strength (Sec 3.5): The strength of an acid is related to its acid dissociation constant, Ka ; the stronger the acid, the larger its Ka, and the smaller its pKa.

Activating group (Sec 15.10, 15.11, Lab 15.5): A substituent that makes the aromatic ring more reactive than benzene, usually referring to electrophilic aromatic substitution.

Activation energy, E_act (Sec 10.5B): The difference in enthalpy, ΔH, of the transition state and the reactants; if a reaction has a very small entropy change, ΔS ≈ 0 , then ΔG ≈ ΔH, and the activation energy is almost the same as the free energy of activation, E_act ≈ ΔG^‡ . Also called energy of activation.

Active hydrogen compound (Sec 18.8): A compound that has two electron-withdrawing groups attached to the same methylene carbon atom, Z-CH₂-Z' , which makes the methylene hydrogen atoms acidic, with a pK_a between 3 and 13. Also called active methylene compound.

Active methylene compound (Sec 19.5): A compound that has two electron-withdrawing groups attached to the same methylene carbon atom, Z-CH₂-Z', which makes the methylene hydrogen atoms acidic, with a pK_a between 3 and 13. Also called active hydrogen compound.

Acylation (Sec 15.7): The introduction of an acyl group into a molecule. Examples include the Friedel-Crafts acylation and the conversion of amines to amides.

Acyl cation (Sec 9.16C, 15.7): The resonance-stabilized cation: R-C⁺=O ↔ R-C≡O⁺ . Also called an acylium ion.

Acyl chloride (Sec 15.7, 17.2G, 17.5): An activated carboxylic acid derivative in which the hydroxyl group of the acid is replaced by a chlorine atom, RCOCl. Also called acid chloride.

Acyl compound (Sec 17.1): A compound containing an acyl group, (R-C=O)- ; it is usually derived from a carboxylic acid, such as an ester, acyl halide, amide, or carboxylic acid anhydride.

Acyl group (Sec 15.7, 16.2, 17.1): A functional group consisting of a carbonyl group, >C=O, which is attached to an alkyl or aryl group, -C(=O)R; it is often added by reaction with a carboxylic acid derivative. Also called an alkanoyl group.

Acyl halide (Sec 15.7, 17.2G): A general name for an activated carboxylic acid derivative, in which the hydroxyl group of the acid is replaced by a halogen atom, RC(O)X. Also called an acid halide.

Acyl transfer reaction (Sec 17.4): Two-stage addition-elimination reaction in which one type of carboxylic acid derivative is converted to another. In the addition stage, the nucleophile adds to the carbon that bears the leaving group. In the elimination stage, the leaving group is expelled. Also called a nucleophilic acyl substitution reaction.

Acylation of ketone enolates (Sec 19.3): Nucleophilic substitution reactions between a ketone enolate ion and an ester, to produce a β-dicarbonyl compound.

Acylium ion (Sec 9.16C, 15.7): The resonance-stabilized cation: R-C⁺=O ↔ R-C≡O⁺ . Also called an acyl cation.

Addition-elimination mechanism (Sec 18.4, 21.11A): Two-stage mechanism for nucleophilic acyl substitution reactions and nucleophilic aromatic substitution (S_NAr) reactions; in the addition stage, the nucleophile adds to the carbon that bears the leaving group, then in the elimination stage, the leaving group is expelled.

Addition polymer (Sec 10.11): A polymer that results from a stepwise addition of monomers to a chain (usually through a chain reaction) with no loss of other atoms or molecules in the process. Also called a chain-growth polymer.

Addition reaction (Sec 8.1, 12.1): A reaction which increases the number of atoms or groups that are attached to a pair of atoms joined by a double or triple bond; all parts of the adding reagent appear in the product, and two molecules become one.

Adduct (Sec 13.10): (1) The product of a Diels-Alder reaction. (2) The product of an addition reaction that contains all atoms of both reactants, with the formation of two new sigma bonds and the loss of two pi bonds.

Adhesion: The force between unlike molecules.

Adsorbent (Lab 6.3): A substance that adsorbs by attaching other substances to its surface without any covalent bonding.

Adsorption (Lab 5.3): The selective attraction of a substance in a liquid or gaseous mixture to the surface of a solid.

Aerosols: Dispersions of liquids in gases and solids in gases.

Aglycone (Sec 22.4): The alcohol obtained by hydrolysis of a glycoside.

Alcohol (Sec 2.6, 4.3F, 11.1): Molecule containing a hydroxyl group, -OH , bound to a sp³ hybridized carbon atom, with the general formula ROH.

Aldaric acid (Sec 22.6C): Carbohydrate in which carboxylic acid functions are present at both ends of the chain, α, ω-dicarboxylic acid, that results from nitric acid oxidation of the aldehyde group and the terminal alcohol group of an aldose.

Aldehyde (Sec 2.9, 12.1, 16.1): A molecule containing a terminal carbonyl group, >C=O , that is attached to one hydrogen and one other carbon atom, with the general formula RCHO.

Aldehyde hydrate (Sec 16.7A): The product of the nucleophilic addition of one molecule of water to an aldehyde; the hydrate has two hydroxyl groups, -OH, on the former carbonyl carbon atom; this product is a terminal gem-diol (1,1-diol).

Alditol (Sec 22.7): The alcohol that results from the reduction of the carbonyl group of a carbohydrate.

Aldol (Sec 19.4, Lab 18.3): A compound that is both an aldehyde (or ketone) and an alcohol; most aldols are β-hydroxy aldehydes or β-hydroxy ketones.

Aldol condensation (Sec 19.1, 19.4, Lab 18.3): An aldol addition reaction followed by dehydration to produce an α,β-unsaturated aldehyde or α,β-unsaturated ketone, which is catalyzed by an acid, or by a base with heat.

Aldol cyclization (Sec 19.6): An intramolecular aldol condensation of a dicarbonyl compound, usually a keto aldehyde, to form a five- or six-membered ring.

Aldol reaction (Sec 19.4 - 19.6): An acid- or base-catalyzed nucleophilic addition of the enolate of an aldehyde (or ketone) to the carbonyl carbon atom of an aldehyde (or ketone) to produce an aldol (β-hydroxy aldehyde or β-hydroxy ketone). Also called aldol addition reaction.

Aldonic acid (Sec 22.6C): A monocarboxylic acid that results from oxidation of the aldehyde group of an aldose.

Aldose (Sec 22.2): Carbohydrate that contains an aldehyde carbonyl group in its open-chain form.

Alicyclic: Term describing an aliphatic cyclic structural unit.

Aliphatic compound (Sec 14.1): A nonaromatic compound such as an alkane, cycloalkane, alkene, alkyne, or one of their derivatives.

Alkadiene (Sec 13.6): Hydrocarbon that contains two C=C double bonds. Also called a diene.

Alkali metals: Group I in the periodic table.

Alkaline earth metals: Group II in the periodic table.

Alkaloid: An amine that occurs naturally in many plants, fungi and bacteria, and has profound physiological effects on animals, often toxic; the name derives from the word alkaline, since these compounds are weak bases with a bitter taste.

Alkane (Sec 2.1A, 4.1 - 4.3, 4.7, 4.16): Saturated hydrocarbon that contains only single covalent bonds; it has the general molecular formula C_nH_2n+2 .

Alkanedioic acid (Sec 18.2D): A dicarboxylic acid.

Alkanethiolate: The conjugate base RS^- , formed by deprotonating a thiol, RSH.

Alkanide migration (Sec 7.8A): Migration of a alkanide ion, RH₂C:^- , from a carbon adjacent to a carbocation, which usually forms a more stable carbocation. Also called alkanide rearrangement.

Alkene (Sec 2.1, 4.1): Unsaturated hydrocarbon that contains at least one C=C double covalent bond; its molecular formula loses two hydrogen atoms for every double bond, as compared to the corresponding alkane. Also called an olefin.

Alkene stability (7.3B): The greater the number of attached alkyl groups (the more highly substituted the alkene), the greater the alkene's stability.

Alkoxide ion (Sec 3.15, 6.15B, 11.6): A deprotonated alcohol, RO^- , with a negative charge on the oxygen atom, which is the conjugate base of an alcohol, ROH.

Alkoxy group (Sec 11.2): The RO- group; obtained by removing a hydrogen atom from an alcohol, ROH.

Alkylamine (Sec 20.1): An amine that has one or more alkyl groups attached to the amine nitrogen, such as RNH₂ .

Alkylation (Sec 7.11, 15.6, 18.4): The introduction of an alkyl group into a molecule.

Alkylcuprate: An organocopper reagent, such as RCu or R₂CuLi, that add the alkyl group to α,β-unsaturated ketones in 1,4 (conjugate) addition reactions.

Alkyl group (Sec 2.4, 4.3): Group obtained by removing a hydrogen atom from an alkane; abbreviated R.

Alkyl halide (Sec 2.5, 4.3E, 6.1): Compound in which a halogen atom (F, Cl, Br, I) replaces a hydrogen atom of an alkane, with the general formula RX. Also called haloalkane.

Alkyl hydrogen sulfate (Sec 8.4): The Markovnikov addition product, R-OSO₃H, from the reaction of cold concentrated sulfuric acid, H₂SO₄ , with the C=C group of an alkene.

Alkyloxonium ion (Sec 3.13, 7.7, 11.5): A protonated alcohol, RO⁺H₂ , with a positive charge on the oxygen atom, which is the conjugate acid of an alcohol, ROH.

Alkyne (Sec 2.1C, 4.1, 4.6): Unsaturated hydrocarbon that contains at least one C≡C triple covalent bond; its molecular formula loses four hydrogen atoms for every triple bond, as compared to the corresponding alkane.

Allene (Sec 13.6): A compound containing cumulated C=C double bonds, H₂C=C=CH₂ . Also called a cumulene.

Allomorph: Any of two or more crystalline forms of a substance

Allotropes: Different forms of an element in the same state; e.g., white phosphorus and red phosphorus.

Alloy: A mixture of two or more metals that usually is stronger and harder than any of the pure metals.

Allyl cation (Sec 13.3): The propenyl cation, ⁺CH₂-CH=CH₂ , that is formed by removing a proton from the methyl group of propene, and is stabilized by delocalization of the positive charge by resonance.

Allyl group (Sec 4.5, 13.1): The common name for the 2-propenyl group, H₂C=CHCH₂─

Allyl radical (Sec 10.8A, 13.3): The free-radical ∙CH₂- CH=CH₂ that is stabilized by delocalization of electrons through resonance.

Allylic cation (Sec 13.1, 13.9, 15.15): A general term for any carbocation that has a carbon atom with a positive charge that is singly bound to a C=C double bond, with the general formula ⁺CR₂-C(R)=CR₂ ; substituted allylic cations are more stable than any saturated carbocation due to delocalization of the positive charge through resonance.

Allylic hydrogen (Sec 13.2): A hydrogen atom on any saturated carbon atom that is adjacent to a C=C double bond.

Allylic position (Sec 10.8, 13.1): The single-bonded carbon atom that is adjacent to a C=C double bond. This term is used in naming compounds, such as an allylic halide, or in referring to reactive intermediates, such as an allylic cation, an allylic radical, or an allylic anion.

Allylic radical (Sec 13.2A): A general term for any free-radical that has a carbon atom with an

unpaired electron that is adjacent to a C=C double bond, with the general formula ∙CR₂- C(R)=CR₂ ; allylic radicals are more stable than any saturated radical due to delocalization of electrons by resonance.

Allylic shift (Sec 13.3): The isomerization of a double bond that occurs through the delocalization of an allylic intermediate.

Allylic substituent (Sec 13.2): Refers to a substituent on a carbon atom adjacent to a carbon-carbon double bond.

Allylic substitution reaction (Sec 10.8): A reaction in which an allylic hydrogen atom is replaced by a nucleophile.

Alpha (α) carbon atom (Sec 17.1): The carbon atom next to a carbonyl group. The hydrogen atoms on the α carbon are called α hydrogens or α protons.

Alpha substitution (Sec 18.3): Replacement of a hydrogen atom on the α carbon atom of a carbonyl compound by some other group. Also called α substitution

Amalgam (Sec 15.9): An alloy of a metal with mercury.

Ambident nucleophile: Nucleophiles capable of reacting at two different nucleophilic sites.

Amide (Sec 2.10C, 17.2H, 17.8, Lab 20.3): A molecule containing a carbonyl group, >C=O , that is attached to an amino group, -NR₂ , with the general formula RCONR₂' (R may be hydrogen); often formed by the reaction of a carboxylic acid and an amine, with loss of water.

Amine (Sec 2.8, 20.1): A molecule containing an amino group, -NH₂ , -NHR, or -NR₂ , obtained by removing one or more hydrogen atoms from ammonia, with the general formula RNH₂ , RNHR, or RNR₂ . A primary amine has one R group attached to the N atom, a secondary amine has two R groups attached to the N atom, and a tertiary amine has three R groups attached to the N atom.

Amino acids (Sec 24.2): The basic building blocks of proteins that contain both an amine group and a carboxylic acid group, H₂N-CH(R)-COOH.

Amino group (Sec 20.1): The -NH₂ group; if alky1ated, it becomes an alkylamino group -NHR, or a dialkylamino group -NR₂ .

Aminoalcohol (Sec 16.8A, 20.5C): An intermediate in the reaction of an aldehyde or ketone with a primary amine to form of an imine, which has a hydroxyl group and an amine bonded to the same carbon atom. Also called a hemiaminal, or carbinolamine.

Amino sugar (Sec 22.15B): Carbohydrate in which one of the hydroxyl groups has been replaced by an amino group.

Ammonium salt (Sec 20.3D): A derivative of an amine with a positively charged nitrogen atom having four bonds; an amine is protonated by an acid to give an ammonium salt: RNH₂ + HA → RN⁺H₃ A^- ; a quaternary ammonium salt has a positively charged nitrogen atom bonded to four alkyl (or aryl) groups: R₄N⁺. Also called aminium salt, or amine salt.

Amphipathic (Sec 2.13D, 23.2C): A molecule that contains both hydrophilic and hydrophobic groups, such as a soap or phospholipid.

Amphiphilic: Possessing both hydrophilic and lipophilic properties within the same species.

Amphoteric: A compound that can function as either an acid or a base. Also called amphiprotic.

Amylopectin (Sec 22.13A): A polysaccharide present in starch; a polymer of α(1,4)-linked glucose units, with branches of 24-30 glucose units connected to the main chain by an α(1,6) linkage.

Amylose (Sec 22.13A): The water-dispersible component of starch; a polymer of α(1,4)-linked glucose units.

Anabolic steroid (Sec 23.4): A steroid that promotes muscle growth.

Androgen (Sec 23.4): A male sex hormone.

Angle strain (Sec 4.10): The strain a molecule possesses because its bond angles are distorted from their normal values; measured by the increased potential energy of a molecule (usually cyclic) caused by deformation of a bond angle away from its lowest energy value.

Anhydride (acid anhydride) (Sec 18.2F): A composite of two acid molecules, with loss of water. A mixed anhydride contains two different acids.

Anion: Negatively charged ion.

Anionic polymerization (Sp. Topic A): A polymerization in which the reactive intermediates are negatively charged.

Annulene (Sec 14.7B): Monocyclic hydrocarbon characterized by a completely conjugated system of double bonds, which may or may not be aromatic. The ring size of an annulene is represented by a number in brackets. For example, benzene is [6]annulene, and 1,3,5,7-cyclooctatetraene is [8]annulene.

Anomers (Sec 22.2C): A term used in carbohydrate chemistry. Anomers are diastereomers that differ only in configuration at the acetal or hemiacetal carbon of a sugar in its cyclic form.

Anti 1,2-Dihydroxylation (Sec 11.15): A series of two reactions for the anti addition of two hydroxyl groups, -OH, to opposite sides of adjacent carbons in a C=C group of an alkene; the first reaction is the epoxidation of the alkene with a peroxy acid to give an epoxide, then the second reaction is the acid-catalyzed hydrolysis of the epoxide, which produces a 1,2-diol (glycol); a cyclohexene will be converted into a trans-1,2-diol.

Anti addition (Sec 7.13A, 7.14, 8.11): An addition reaction that places the parts of the adding reagent on opposite faces of the reactant.

Antiaromatic (Sec 14.7E): A planar cyclic conjugated system that is destabilized by electron delocalization, and its pi electron energy is greater than that of a corresponding open-chain compound.

Antibonding molecular orbital (Sec 1.11, 1.15): A molecular orbital whose energy is higher than that of the isolated atomic orbitals from which it is constructed. Electrons in an antibonding molecular orbital destabilize the bond between the atoms that the orbital encompasses.

Anticodon (Sec 25.5C): A sequence of three bases on transfer RNA (tRNA) that associates with a codon of messenger RNA (mRNA).

Anti conformation (Sec 4.9): A staggered conformation of a molecule in which the two largest substituents on adjacent atoms are the maximum distance apart, with a dihedral angle between their bonds of 180°.

Anti coplanar (Sec 7.6C): The five atoms involved in the transition state of an E2 reaction must be coplanar, for proper overlap of orbitals in the developing pi bond of the alkene that is being formed. The anti coplanar transition state is the preferred orientation, because the base and leaving group are anti (staggered), and they are separated by the greatest distance.

Anti-Markovnikov addition (Sec 8.2D, 8.7 - 8.9, 8.19, 10.9): A radical addition reaction between hydrogen bromide, HBr, and an unsymmetrical alkene in the presence of peroxides, ROOR, where the hydrogen adds to the more substituted carbon, and the bromine adds to the less substituted carbon, which produces the less substituted alkyl bromide.

Antioxidant (Sec 10.11D): A compound that inhibits autoxidation and traps free radicals.

Aprotic solvent (Sec 6.13C): A solvent that does not have acidic protons.

Arene (Sec 15.12): A general name for an aromatic hydrocarbon, abbreviated ArH.

Arenium ion (Sec 15.2, Lab 15.2): A nonaromatic, resonance-stabilized cyclohexadienyl carbocation intermediate that is formed when the pi system of benzene attacks an electrophile. Also called a σ-complex.

Aromatic (Sec 2.2D, 14.1 - 14.11, Lab 15): A planar cyclic conjugated system that is stabilized by electron delocalization; its pi electron energy is less than that of a corresponding open-chain compound; it has a large resonance energy; it reacts by substitution rather than addition; in the ^lH NMR spectrum, protons exterior to the ring are deshielded.

Aromatic compound (Sec 2.1, 14.1 - 14.8, Lab 15): A planar cyclic conjugated system that is stabilized by electron delocalization.

Aromatic halogenation (Sec 15.3, Lab 15.5): Replacement of an aromatic ring hydrogen atom by a halogen atom (F, Cl, Br, or I ); aromatic chlorination and aromatic bromination require a lewis acid catalyst.

Aromatic hydrocarbon (Sec 2.1D, 14.1 to 14.11, Lab 15): A planar cyclic conjugated system, with alternating single and double bonds in the ring, that is stabilized by electron delocalization.

Aromatic ion (Sec 14.7D): A planar cyclic conjugated ion that is stabilized by electron delocalization, and its pi electron energy is less than that of a corresponding open-chain ion.

Aromatic nitration (Sec 15.4, Lab 15.4): Replacement of an aromatic ring hydrogen atom by a nitro group, -NO₂ .

Aromatic sulfonation (Sec 15.5): Replacement of an aromatic ring hydrogen atom by a sulfonic acid group, -SO₃H .

Aromaticity (Sec 14.1): Special stability associated with aromatic compounds.

Arrhenius theory of acids and bases (Sec 3.2): An acid is a substance that ionizes in water to produce protons; a base is a substance that ionizes in water to produce hydroxide ions.

Arylamine (Sec 20.1A): An amine that has one or more aromatic groups attached to the amine nitrogen, such as ArNH₂ .

Aryl group (Sec 6.1): The general name for a group obtained by the removal of a hydrogen from a ring position of an aromatic hydrocarbon, abbreviated Ar-.

Aryl halide (Sec 6.1): An organic halide in which the halogen atom is attached to an aromatic ring, such as a benzene ring. Also called haloarene.

Aryne (Sec 21.11B): A species that contains a triple bond within an aromatic ring, such as benzyne.

Asymmetric: Lacking all significant symmetry elements; an asymmetric object does not have a plane, axis, or center of symmetry.

Asymmetric center: Obsolete name for a chirality center.

Atactic polymer: A polymer in which the configuration at the stereogenic centers along the chain is random.

Atom (Sec 1.2): Smallest unit of matter that retains an element's properties; composed of protons, neutrons, and electrons.

Atomic absorption spectrophotometry: Determination of concentration by the ability of atoms to absorb radiant energy of specific wavelengths.

Atomic mass unit: A unit of mass equal by definition to 1/12 of the mass of an atom of carbon-12, which is 1.6605402 × 10^-27 kg. Also called Dalton (Da).

Atomic number, Z (Sec 1.2): The number of protons in the nucleus of a particular atom, which determines the identity of the element.

Atomic orbital (Sec 1.10 - 1.15): A volume of space about the nucleus of a single atom where there is a high probability of finding an electron (or two spin-paired electrons). Abbreviated AO.

Atropisomers (Sec 5.18): Conformational isomers that are stable compounds which can be separated.

Aufbau principle (Sec 1.10A): Electrons are added so that orbitals of lowest energy are filled first.

Autoxidation (Sec 10.12C): Reaction of an organic compound with oxygen to form a hydroperoxide, R-O-OH.

Avogadro’s number: The number of particles in one mole of any substance (6.0221415 × 10²³ )

Axial bond (Sec 4.12): The six bonds of a cyclohexane ring that are perpendicular to the average plane of the ring, and that alternate up and down around the ring.

Azeotrope (Lab 4.4, 10.3): A mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation, because the boiling liquid and vapor have the same ratio of substances.

Azide (Sec 20.4): A compound having the azido group, -N₃ .

Azo coupling: Formation of a compound of the type ArN=NAr' by reaction of an aryl diazonium salt with an arene. The arene must be strongly activated toward electrophilic aromatic substitution; that is, it must bear a powerful electron-releasing substituent such as -OH or -NR₂ .

B

Baeyer-Villiger oxidation: Oxidation of a ketone with a peroxy acid to produce an ester.

Base (Sec 3.2, 3.3): An Arrhenius base is a compound that dissociates in water and releases hydroxide ions; a Brønsted-Lowry base is a proton acceptor; a Lewis base is an electron-pair donor.

Base-catalyzed ring opening of an epoxide (Sec 11.14): In basic solution, a nucleophile attacks an unsymmetrical epoxide primarily at the less substituted carbon of the epoxide by an S_N2 mechanism.

Base dissociation constant, K_b (Sec 3.5): The equilibrium constant for the reaction: B ↔ HB⁺ + OH ^‾ is defined as: K_b = [HB⁺ ] [OH ^‾ ] / [B] and pK_b = -log K_b ; often converted into the pKa of its conjugate acid by the formula: pKa = 14.00 - pK_b .

Base pair (Sec 25.2): Term given to the purine of a nucleotide and its complementary pyrimidine. In DNA, adenine (A) is complementary to thymine (T), and guanine (G) is complementary to cytosine (C).

Base peak (Sec 9.13): The most intense peak detected in mass spectrometry.

Base strength (Sec 3.5): The strength of a base is inversely related to its conjugate acid dissociation constant, Ka ; the stronger the base, the weaker its conjugate acid, thus the smaller its Ka, and the larger its pKa.

Basicity (Sec 6.13B): The strength of a base, as measured by its equilibrium constant for removing a proton from a Brønsted-Lowry acid (a thermodynamic property); the stronger the base, the weaker its conjugate acid, the smaller its Ka, and the larger its pKa.

Beer-Lambert Law (Sec 13.9, Lab 8.4): A physical law stating that the quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is directly proportional to the concentration of the substance and the path length of the light through the solution, according to the equation: A = ε ∙ c ∙ l, where A is the absorbance at a particular wavelength, ε is the extinction coefficient, c is the concentration, and l is the path length in cm of the light beam through the sample cell. Also called Beer's Law

Bending vibrational mode (Sec 2.16, Lab 8.2): Regular, repetitive motion between three atoms connected by covalent bonds, in which the bond angle changes; bending vibrations are one type of molecular motion that gives rise to a peak in the infrared spectrum.

Bending vibrations (Sec 2.15, Lab 8.2): Motions of three atoms in a molecule that result in bond angle deformations due to absorption of IR light.

Benzene (Sec 2.1D, 14.1 - 14.6): An aromatic six-carbon ring with the molecular formula C₆H₆ ; each carbon atom is sp² hybridized with one p orbital that contains one electron. Also called [6]annulene.

Benzene substitution (Sec 14.3): Replacement of a hydrogen on a benzene ring by a strong electrophile.

Benzenoid aromatic compound (Sec 14.8A): A class of aromatic compounds whose molecules have two or more benzene rings fused together. Also called benzenoid polycyclic aromatic hydrocarbons.

Benzoyl group: The C₆H₅CO- group; obtained by removing the hydroxyl group, -OH, from benzoic acid, C₆H₅COOH; abbreviated Bz-.

Benzyl group (Sec 2.4B, 10.9, 14.2): The C₆H₅CH₂- group; obtained by removing a hydrogen atom from the methyl group of toluene, C₆H₅CH₃ . Abbreviated Bn- .

Benzylic cation (Sec 15.15): An unusually stable carbocation, in which the side-chain carbon atom that is directly attached to a benzene ring has a positive charge, Ph-C ⁺ R₂ - .

Benzylic radical (Sec 15.12): An unusually stable free radical, in which the side-chain carbon atom that is directly attached to a benzene ring has an unpaired electron, Ph-C ^∙ R₂ - .

Benzylic substituent (Sec 15.12, 15.15): Refers to a substituent on the side-chain carbon atom that is directly attached to a benzene ring.

Benzyne (Sec 21.11B): Dehydrobenzene, C₆H₄ , in which benzene lacks two hydrogens and has an additional pi bond that results from sideways overlap of two sp² orbitals on adjacent atoms of the ring (usually drawn with a triple bond replacing a double bond); it is a very unstable and highly reactive aromatic intermediate, which is formed during a nucleophilic aromatic substitution (S_NAr) reaction by an elimination-addition mechanism.

Betaine (Sec 16.10): An electrically neutral molecule that has nonadjacent cationic and anionic sites, and that does not possess a hydrogen atom bonded to the cationic site.

Bicyclic compound (Sec 4.4B, 4.14): A molecule with two fused rings that share at least two carbon atoms.

Bimolecular reaction (Sec 6.5): A reaction whose rate-determining step involves two chemical species.

Birch reduction (Sec 15.16): The partial reduction of a benzene ring by sodium or lithium metal in liquid ammonia; the products are usually l,4-cyclohexadienes.

Blocking group (Sec 15.14A): A group that is introduced into a molecule to block the reaction at a particular site, such as a carbon atom, while the reaction is carried out at some other location in the molecule; the blocking group is later removed in a subsequent reaction.

Boat conformation (Sec 4.11): A conformation of cyclohexane that resembles a boat, with eclipsed bonds along its two sides; the boat conformation is less stable (higher energy) than the chair conformation.

Boiling point (Sec 2.13, Lab 4.2): The temperature of a liquid at which the equilibrium vapor pressure equals the total external pressure, and which the rate of evaporation increases dramatically with bubbles forming in the liquid.

Bond angle (Sec 1.17): The angle between two bonds originating at the same atom.

Bond dissociation energy, DH, (Sec 10.2): The standard enthalpy change, ΔH°, that accompanies the homolytic cleavage of a covalent bond.

Bond length (Sec 1.11, 1.14A): The equilibrium distance between two bonded atoms or groups.

Bond-line formula (Sec 1.7C): Organic that shows the carbon skeleton of a molecule with lines; hydrogen atoms are not written in, but all other non-carbon atoms are written in.

Bond order: The number of chemical bonds between a pair of atoms, which is an index of bond strength. In molecular orbital theory, bond order is defined as the difference between the number of bonding electrons and the number of antibonding electrons, divided by two. For example, the bond order for a carbon-carbon bond is 1 for ethane, 2 for ethene, 3 for ethyne, and 1.5 for benzene.

Bonding molecular orbital (Sec 1.11, 1.15): The energy of a bonding molecular orbital is lower than the energy of the isolated atomic orbitals from which it arises. When electrons occupy a bonding molecular orbital, they help to hold together the atoms that the molecular orbital encompasses.

Broadband proton decoupling (Sec 9.11B): A technique in ¹³C NMR spectroscopy that removes the splitting of ¹³C signals caused by coupling of ¹³C and ¹H nuclei, which causes all of the ¹³C signals to appear as singlets. Also called BB proton decoupling.

Bromination (Sec 8.12, 10.5C, 10.6A): A reaction in which bromine atoms are introduced into a molecule.

Bromohydrin (Sec 8.13): A bromo alcohol, which contains a bromine atom and a hydroxyl group on adjacent carbons

Bromonium ion (Sec 8.12A): A cation with one positive bromine atom bonded to two adjacent carbons.

Bronsted-Lowry theory of acids and bases (Sec 3.1A): An acid is a substance that can donate (or lose) a proton; a base is a substance that can accept (or remove) a proton. The conjugate acid of a base is the molecule or ion that forms when a base accepts a proton. The conjugate base of an acid is the molecule or ion that forms when an acid loses its proton.

Buffer: A solution that resists changes in pH; contains a weak acid and its conjugate base.

Butyl group (Sec 4.3): The four carbon alkyl group CH₃CH₂CH₂CH₂- . Also called the n-butyl group.

sec-Butyl group (Sec 4.3): The four carbon alkyl group CH₃CH₂CH(CH₃)- . Also called the (1-methylpropyl) group.

tert-Butyl group (Sec 4.3): The four carbon alkyl group (CH₃)₃C- . Also called the (1,1-dimethylethyl) group.

C

Cahn-lngold-Prelog notation (Sec 5.7, 7.2): System for specifying the absolute configuration for R and S, or E and Z stereoisomers, on the basis of the order of attachment of atoms or groups, which are ranked by precedence according to rules based on atomic number.

Calorie (cal): A unit of energy, defined as the heat required to raise the temperature of 1 g of water by 1 °C. The thermochemical calorie is defined as 4.184 J.

Capacitance (C): The amount of electric charge that may be stored upon a body per unit electric potential; measured in farads, where 1 F = 1 C / V.

Carbamate (Sec 17.9A): An ester, ROC(=O)NHR', that is formed by the reaction between an alkyl chloroformate, ROC(=O)Cl, and an amine, R'NH₂ ; it can also be formed by the reaction between an alcohol, ROH, and an isocyanate, R'-N=C=O ; carbamate derivatives formed by reacting an alcohol with α-naphthyl isocyanate are crystalline solids with sharp melting points. Also called an urethane.

Carbamic acid (Sec 17.9A): An amide of carbonic acid, HOC(=O)NH₂

Carbanion (Sec 3.4, 3.8, 12.1A, 12.7): A chemical species in which a carbon atom bears a formal negative charge; the :C ^‾ anion has four sp³ hybrid orbitals with a lone pair of electrons in one of them, and it has a trigonal pyramidal molecular geometry; it can act as a Lewis base, a very strong Brønsted-Lowry base (pKa ≈ 50), and a powerful nucleophile. Common sources of carbanions are organolithium compounds, RLi, and Grignard reagents, RMgX.

Carbene (Sec 8.15): An uncharged species in which a carbon atom is divalent and has a lone pair of electrons, such as methylene, :CH₂ , and it reacts with alkenes by adding to the double bond to form cyclopropane derivatives.

Carbenoid (Sec 8.15C): A carbene-like species, such as the Simmons-Smith reagent which is formed when diiodomethane reacts with a zinc-copper couple, CH₂I₂ / Zn(Cu), and it reacts with alkenes by adding to the double bond to form cyclopropane derivatives.

Carbinolamine (Sec 16.8A, 20.5C): An intermediate in the reaction of an aldehyde or ketone with a primary amine to form of an imine, which has a hydroxyl group and an amine bonded to the same carbon atom. Also called a hemiaminal, or aminoalcohol.

Carbocation (Sec 3.4, 6.11): A chemical species in which a carbon atom bears a formal positive charge; the C⁺ cation has three sp² hybrid orbitals, plus one empty p orbital, and it has a trigonal planar molecular geometry; it can act as a Lewis acid and an powerful electrophile. Also called carbonium ion.

Carbohydrate (Sec 22.1A): A group of naturally occurring compounds that are usually defined as polyhydroxyaldehydes or polyhydroxyketones, or as substances that undergo hydrolysis to yield such compounds. The name carbohydrate comes from the fact that many possess the empirical formula C_x(H₂O)_y .

Carbonate ester (Sec 17.9): A diester of carbonic acid, ROC(=O)OR'.

Carbonic acid (Sec 17.9): The inorganic, weak diprotic acid, HOC(=O)OH, or H₂CO₃ ; its acid dissociation constants are pK_a1 = 6.35 and pK_a2 = 10.2 ; it is formed by the equilibrium reaction between water and carbon dioxide: H₂O + CO₂ ↔ H₂CO₃ .

Carbonyl dichloride (Sec 17.9): The simplest acid chloride, ClCOCl , that is formally derived from carbonic acid. Also called phosgene.

Carbonyl group (Sec 2.9, 12.1, 16.1): A functional group consisting of a carbon atom doubly bonded to an oxygen atom, >C=O.

Carboxyl group (Sec 17.1): A functional group where a terminal carbon is part of a carbonyl group, >C=O, and is bound to a hydroxyl group, -OH, to form a carboxylic acid, RCOOH.

Carboxylate ion (Sec 17.2B): The anion resulting from deprotonation of a carboxylic acid, RCOO‾ ; it is isolated as the salt of the carboxylic acid.

Carboxylation (Sec 17.3): A reaction in which a carboxylic acid group is introduced in a substrate, such as the addition of CO₂ to a Grignard reagent: RMgX + CO₂ → RCOOH. Also called carbonation.

Carboxylic acid (Sec 2.10A, 12.2, 17.2A): Molecule containing a carbonyl group, >C=O , that is attached to a hydroxyl group, -OH , which is called a carboxyl group, -COOH, with the general formula RCOOH.

Carboxylic acid derivative (Sec 17.1): Compound that yields a carboxylic acid on hydrolysis, such as esters, acid anhydrides, acyl chlorides, amides, and nitriles.

Carboxylic acid anhydride (Sec 17.2F, 17.6): An activated carboxylic acid derivative formed from two acid molecules with loss of a molecule of water; a mixed anhydride is derived from two different carboxylic acid molecules. Also called carboxylic anhydride, or acid anhydride.

Carboxylic ester (Sec 2.10B, 12.1, 17.2E): A molecule containing a carbonyl group, >C=O , that is attached to an alcohol group, -OR' , with the general formula RCOOR' , which may be formed by the reaction of a carboxylic acid and an alcohol with the loss of water, H-OH. Also called an ester.

Cascade polymer: A polymer produced from a multifunctional central core by progressively adding layers of repeating units.

Catalyst: A substance that increases the rate of a chemical reaction, without being consumed.

Cation: Positively charged ion.

Cellulose (Sec 22.13C): A polysaccharide in which thousands of glucose units are joined by β(1,4) linkages.

CFC (Sec 10.12D): A chlorofluorocarbon, such as freon.

Chain-growth polymer (Sec 10.11): A polymer that results from the stepwise addition of monomers to a growing chain (usually through a chain reaction), with no loss of other atoms or molecules in the process. Also called an addition polymer.

Chain reaction (Sec 10.4 - 10.6, 10.10, 10.11): A reaction that proceeds by a sequential, stepwise mechanism, in which each step generates the reactive intermediate that causes the next step to occur; the mechanism involves chain initiating steps, chain propagating steps, and chain terminating steps.

Chair conformation (Sec 4.11): A conformation of cyclohexane that resembles a chair, which is free of angle strain because all C-C-C bond angles are 109.5°, and is free of torsional strain because all bonds are staggered; it is the most stable (lowest energy) conformation of cyclohexane.

Chemical bond: A connection between atoms.

Chemical shift (Sec 9.2A, 9.7, 9.11C, Lab 8.3): The position of a signal along the horizontal axis of a NMR spectrum at which a nucleus absorbs relative to a reference compound such as tetramethylsilane (TMS), and measured as delta values.

Chemically equivalent protons (Sec 9.8, Lab 8.3): In ¹H NMR, protons that are in exactly the same chemical environment will behave the same in chemical reactions, will have identical chemical shifts, and give only one ¹H NMR signal.

Chirality (Sec 5.1, 5.4, 5.6): The property of nonidentity of an object with its mirror image.

Chirality center (Sec 5.4, 5.6, 5.17): A tetrahedral atom with four different groups attached to it, so that interchanging any two groups produces a stereoisomer.

Chiral molecule (Sec 5.3, 5.10, 5.12): A molecule that is not superposable on its mirror image, that has handedness, and an enantiomer of the molecule exists.

Chlorination (Sec 8.12, 10.3 - 10.5): A reaction in which one or more chlorine atoms are introduced into a molecule.

Chloroform (Sec 17.3C): Compound formed by replacing three hydrogen atoms in methane, CH₄ , with chlorine atoms to form CHCl₃ .

Chlorohydrin (Sec 8.14): A chloro alcohol, which contains a chlorine atom and a hydroxyl group on adjacent carbons.

Chromatography (Lab 6.2, 6.3, 6.4): A method for separation and analysis of mixtures based on the different rates at which different compounds are removed from a stationary phase (adsorbent) by a mobile phase (eluting solvent).

Chromic acid reagent (Sec 12.4C): The solution formed by adding sodium or potassium dichromate (and a small amount of water) to concentrated sulfuric acid.

Chromic acid test (Sec 12.4C, Lab 25.7D, 25.11A): When a primary or secondary alcohol is warmed with the chromic acid reagent, the orange color changes to green or blue. A nonoxidizable compound (such as a tertiary alcohol, a ketone, or an alkane) produces no color change.

Chromophore (Lab 8.4): The functional group of a molecule that is responsible for its absorption peak in a UV -Visible spectrum.

cis- (Sec 1.13B, 4.5, 4.13, 5.2, 7.2): Stereochemical prefix indicating that two substituents are on the same side of a double bond or ring.

cis-trans Isomers (Sec 1.13B, 4.5, 4.13, 5.2, 7.2): Diastereomers that differ in their stereochemistry at adjacent atoms of a double bond or on different atoms of a ring; the cis-isomer has two substituents on the same side of a double bond or ring; the trans-isomer has two substituents on opposite sides of a double bond or ring. Also called geometric isomers.

Claisen condensation (Sec 19.2): Base-catalyzed condensation of an ester containing two α-hydrogens with a molecule of the same ester to produce a β-keto ester; the overall reaction involves loss of an α-hydrogen from one ester and loss of an ethoxide ion from the other ester. Also called acetoacetic ester condensation.

Claisen rearrangement (Sec 21.9): (1) The conversion of allyl phenyl ethers to o-allyl phenols by a sigmatropic rearrangement, which proceeds via a cyclohexadienone intermediate. (2) The conversion of allyl vinyl ethers to γ,δ-unsaturated carbonyl compounds by a sigmatropic rearrangement.

Claisen-Schmidt condensation (Sec 19.5A): A base-catalyzed aldol condensation of an aromatic aldehyde with a ketone (or aliphatic aldehyde) to produce an α,β-unsaturated ketone (or α,β-unsaturated aldehyde).

Clemmensen reduction (Sec 15.9): The reduction of a carbonyl group to a methylene group by amalgamated zinc, Zn(Hg), in dilute hydrochloric acid, HCl.

Codon (Sec 25.5C): A sequence of three bases on messenger RNA (mRNA) that contains the genetic information for one amino acid. The codon associates, by hydrogen bonding, with an anticodon of a transfer RNA (tRNA) that carries the particular amino acid for protein synthesis on the ribosome.

Collins Oxidation: The use of a complex of chromium trioxide, CrO₃ , and pyridine, C₅H₅N, in a solvent of dichloromethane, CH₂Cl₂ , to oxidize primary alcohols to aldehydes, and to oxidize secondary alcohols to ketones, but it will not react with carbon-carbon double and triple bonds.

Collins reagent (Sec 12.4): A complex of chromium trioxide with pyridine, CrO₃ ∙ 2 pyridine, used to oxidize primary alcohols selectively to aldehydes.

Combination band in IR: A weak absorption in the IR spectrum that occurs at approximately the sum of the vibration frequencies of two strong absorptions.

Combustion: Burning of a substance in the presence of oxygen. All hydrocarbons yield carbon dioxide and water when they undergo combustion.

Common name: Name given to a compound on some basis other than a systematic set of rules.

Compound (Sec 1.2): Substance composed of two or more different elements that are chemically bound.

Concerted reaction (Sec 6.6): A reaction in which bond breaking and bond forming occur simultaneously (in concert) through a single transition state.

Condensation polymer (Sec 17.12): A polymer produced when bifunctional monomers react with each other through the intermolecular elimination of water or an alcohol. Examples are polyesters, polyamides, and polyurethanes. Also called a step-growth polymer.

Condensation reaction (Sec 17.12, 19.1 - 19.4): A reaction that joins two molecules, with the loss of water or an alcohol. Also called a dehydration synthesis reaction when water is lost.

Condensed structural formula (Sec 1.7B): Organic formula where the atoms that are attached to a carbon are usually written immediately after that carbon, listing hydrogens first.

Configuration (Sec 5.7, 5.15, 6.8): The particular arrangement of atoms (or groups) in space that is characteristic of a given stereoisomer.

Conformations (Sec 4.8): The temporary molecular shapes that result from rotation about the single bonds in a molecule.

Conformational analysis (Sec 4.8, 4.9, 4.11, 4.12): An analysis of the energy changes that occur as a molecule undergoes rotations about its single bonds.

Conformational stereoisomers (Sec 4.9A, 5.14A): Two stereoisomers whose three-dimensional structures differ only due to rotations about single bonds, and they are interconvertible by bond rotations.

Conformers (Sec 4.8): Each possible temporary structure that result from rotation about the single bonds in a molecule.

Conjugate acid (Sec 3.1A, 3.5, Lab 5.3): A compound or ion that forms from the protonation of a base, which converts B into HB⁺ , or converts B ^‾ into HB.

Conjugate acid-base pair (Sec 3.5, Lab 5.3): Two compounds that differ only in the presence or absence of a hydrogen ion; the strength of a conjugate acid is inversely related to the strength of its conjugate base; stronger acids have weaker conjugate bases, and vice versa.

Conjugate addition (Sec 13.9, 19.1, 19.7): An addition reaction in which two groups add to atoms that bear a 1,4-relationship in a conjugated system, which is energetically favored and under thermodynamic control; in α,β-unsaturated carbonyl compounds, a nucleophile adds to the β carbon and the carbonyl oxygen is protonated. Also called 1,4-addition.

Conjugate base (Sec 3.1A, 3.5, Lab 5.3): A compound or ion that forms from the deprotonation of an acid, which converts HA into A^‾ , or converts HA⁺ into A.

Conjugated diene (Section 13.5): System of the type C=C- C=C, in which two pairs of doubly bonded carbons are joined by a single bond; the pi bonding orbitals overlap with each other, and the pi electrons are delocalized by resonance over the four consecutive sp² hybridized carbons

Conjugated double bonds (Sec 13.5): Double bonds that alternate with single bonds; the pi bonding orbitals overlap with each other, and the pi electrons are delocalized by resonance over the consecutive sp² hybridized carbons.

Conjugated unsaturated system (Sec 13.1): Molecules or ions that have a p orbital on an atom adjacent to a multiple bond, which forms an extended pi system; the p orbital may be that of another multiple bond or that of a radical, carbocation, or carbanion.

Conjugation energy (Sec 13.7, 14.5): The energy of stabilization that represents the difference in energy between the actual molecule or ion and that calculated for any resonance structure; this lower energy state arises from delocalization of electrons in the conjugated system, and it results in resonance stabilization.

Connectivity (Sec 1.6, 1.7): The sequence, or order, in which the atoms of a molecule are attached to each other.

Constitutional isomers (Sec 1.6, 4.2, 5.2): Compounds that have the same molecular formula, but that differ in their connectivity, i.e., their atoms are connected in different ways. Also called structural isomers.

Cope elimination (Sec 20.12B): Pyrolysis of a tertiary amine oxide into an alkene and a hydroxylamine.

Coplanar (Sec 7.6D): A conformation in which two adjacent atoms, and two of the vicinal groups that are bound to them, all lie in the same plane. Also called periplanar.

Copolymer: A polymer synthesized by polymerizing two different monomers.

Corey-House synthesis: The reaction of a lithium dialkyl cuprate with an alkyl halide to form a new alkane: R₂CuLi + R'-X → R-R' . Also called the Corey-Posner-Whitesides-House synthesis.

COSY (Sec 9.12): A 2D NMR technique that correlates the chemical shifts of spin-coupled nuclei. Also called correlation spectroscopy.

Coulomb's Law: The force, F, exerted by one charged object on another is proportional to the product of the charges, Q, in coulombs, and inversely proportional to the square of the distance, d, that separates them, in meters: F = k ∙ Q₁ ∙ Q₂ / d² , where Coulomb's constant, k = 8.9875 x 10⁹ N ∙ m² / C² .

Coupling constant, J_ab (Sec 9.9, Lab 8.3): The separation of the peaks of a multiplet, measured in hertz, which is caused by spin-spin coupling between the atoms labeled a and b.

Covalent bond (Sec 1.3B): A chemical bond formed when atoms share electrons.

Cracking (Sec 4.1): A process used in the petroleum industry for breaking down the molecules of larger alkanes into smaller ones. Cracking may be accomplished with heat (thermal cracking), or with a catalyst (catalytic cracking).

Crossed aldol condensation (Sec 19.5): A crossed aldol addition reaction followed by dehydration to produce an α,β-unsaturated aldehyde or α,β-unsaturated ketone; only practical when one reactant has no α hydrogen.

Crossed aldol reaction (Sec 19.5): An aldol addition reaction between two different aldehydes or ketones; this reaction is practical only when one reactant has no α hydrogen. Also called crossed aldol addition reaction.

Crossed Claisen condensation (Sec 19.2): A Claisen condensation between an ester with no α-hydrogens, and a different ester with two or more α-hydrogens.

Crown ether (Sec 11.16): A cyclic polyether that has the ability to form a complex with a metal cation; crown ethers are named as x-crown-y, where x is the total number of atoms in the ring, and y is the number of oxygen atoms in the ring.

Cumulated diene (Sec 13.5): Diene of the type C=C=C, in which one carbon has double bonds to two others.

Cumulated double bonds (Sec 13.5): Successive double bonds with no intervening single bonds.

Cumulene (Sec 13.5): A compound containing cumulated carbon-carbon double bonds. Also called an allene.

Curtius rearrangement (Sec 20.4E): Conversion of a carboxylic acid to an amine having one fewer carbon atoms, which proceeds via thermal decomposition of an acyl azide into an isocyanate. Also called Curtius reaction.

Curved arrow notation (Sec 1.8, 3.2, 10.1): Shows the direction of electron flow in a reaction; the curved arrow begins with a covalent bond or lone pair of electrons, then points towards the site of electron deficiency; a double-barbed arrow represents two electrons, and a single-barbed arrow represents one electron.

Cut-off point of a solvent (Lab 8.4): Minimum wavelength where a solvent is usable for UV-Visible spectroscopy; at lower wavelengths, the solvent has appreciable absorption and is not useful.

Cyanohydrin (Sec 16.9, 17.3): A compound with a hydroxyl group and a cyano group on the same carbon atom, R₂C(OH)(CN), derived by adding HCN to an aldehyde or ketone.

Cycloaddition (Sec 13.10): A reaction, like the Diels-Alder reaction, in which two connected groups add to the end of a pi system to generate a new ring.

Cycloalkane (Sec 4.1, 4.4, 4.7, 4.11): Alkane in which at least some of the carbon atoms are arranged in a ring.

Cycloalkene (Sec 7.4): A cyclic hydrocarbon characterized by a double bond between two of the ring carbons.

Cycloalkyne (Sec 7.4): A cyclic hydrocarbon characterized by a triple bond between two of the ring carbons.

Cyclohexadienyl anion (Sec 21.11A): An intermediate that is resonance stabilized by delocalization of electrons, which is formed during a nucleophilic aromatic substitution (S_NAr) reaction by an addition-elimination mechanism. Also called Meisenheimer intermediate.

Cyclohexadienyl cation (Sec 15.2): The key intermediate in electrophilic aromatic substitution reactions. Also called an arenium ion.

Cyclohexane (Sec 4.4, 4.11 - 4.13): A cyclic form of hexane in which all of the carbon atoms are arranged in a ring.

Cyclohexane conformations (Sec 4.11 - 4.13): The three-dimensional structures of cyclohexane that result from rotations about its single bonds; the most stable form is the chair conformation, followed by the twist boat, the boat, and the half chair which is the most unstable form.

D

d Orbitals (Sec 1.10): A set of five degenerate (equal energy) atomic orbitals; the principal quantum number n > 3; the azimuthal quantum number l = 2; the magnetic quantum numbers m are +2, +1, 0, -1, -2.

D and L designations (Sec 22.2B): A method for designating the configuration of monosaccarides and other similar compounds in which the reference compound is (+)- or (-)-glyceraldehyde. According to this system, (+)-glyceraldehyde is designated D-(+)-glyceraldehyde and (- )-glyceraldehyde is designated L-(- -glyceraldehyde. Therefore, a monosaccharide whose highest numbered stereogenic center has the same general configuration as D-(+)-glyceraldehyde is designated a D-sugar; one whose highest numbered stereogenic center has the same general configuration as L-(+)-glyceraldehyde is designated an L-sugar.

Dalton's Law (Lab 4.2, 4.3): (Also called Dalton's Law of Partial Pressures) When a mixture contains two or more volatile components, the total vapor pressure is equal to the sum of the partial vapor pressures of each such component: P_TOT = P_X + P_Y + P_Z + ...

Deactivating group (Sec 15.10, 15.11, Lab 15.5): A substituent that makes the aromatic ring less reactive than benzene, usually referring to electrophilic aromatic substitution.

Debromination (Sec 7.9): The elimination of two atoms of bromine from a vic-dibromide, or, more generally, the loss of bromine from a molecule.

Debye (D) (Sec 2.3): The unit in which dipole moments, μ, are stated, where 1 D = 1 x 10^-18 esu ∙ cm = 3.336 x 10^-30 C ∙ m (coulomb meter).

Decarboxylation (Sec 17.10): (1) A chemical reaction that releases carbon dioxide. (2) A reaction whereby a carboxylic acid, RCOOH, loses a carboxyl group, -COOH, as carbon dioxide, O=C=O .

Decarboxylation of β-keto acids (Sec 17.10, 18.6): A reaction whereby a β-keto carboxylic acid, or a β-dicarboxylic acid, loses a carboxyl group as carbon dioxide, CO₂ .

Degenerate orbitals (Sec 1.10): Orbitals of equal energy. For example, the three 2p orbitals are degenerate.

Dehydration (Sec 7.7, 7.8, 11.11A): Removal of -OH and -H substituents from nearby atoms; commonly employed in the preparation of alkenes and ethers by heating alcohols in the presence of an acid catalyst.

Dehydration reaction (Sec 7.7, 7.8): An elimination that involves the loss of a molecule of water from the substrate.

Dehydrobenzene (Sec 21.11B): Benzyne, C₆H₄ , in which benzene lacks two hydrogens and has an additional pi bond that results from sideways overlap of two sp² orbitals on adjacent atoms of the ring (usually drawn with a triple bond replacing a double bond); it is a very unstable and highly reactive aromatic intermediate, which is formed during a nucleophilic aromatic substitution (S_NAr) reaction by an elimination-addition mechanism.

Dehydrogenation: (1) Oxidation of a compound by removing a pair of hydrogen atoms, H∙ , or by removing both a hydride ion, :H^- , and a hydrogen ion, H⁺ . (2) An elimination reaction that creates a double bond by removing a pair of hydrogen atoms, H∙ , from adjacent atoms.

Dehydrohalogenation (Sec 6.15A, 7.6): An elimination reaction that results in the loss of hydrogen halide, HX, from adjacent carbon atoms of an alkyl halide, with the formation of a pi bond.

Delocalization (Sec 1.8, 2.1D, 3.10A, 6.11B, 7.7B, 13.3 - 13.7, 14.6): The dispersal of electron density or electrical charge by resonance, which always stabilizes a system.

Delocalization effect (Sec 3.10A, 6.11B): An effect by which resonance causes the dispersal of electron density or electrical charge into two or more atoms, which always stabilizes a system.

Delocalized orbital (Sec 13.3, 13.4): A molecular orbital that results from the combination of three or more atomic orbitals; when filled, these orbitals spread electron density over all the atoms involved.

Delta-scale, δ (Sec 9.7, Lab 8.3): Horizontal scale in NMR that shows the location of signals relative to the internal tetramethylsilane (TMS) standard, which is set at 0. The delta value (in ppm) is found by dividing the chemical shift (in Hz) by the oscillator frequency (in Hz) and multiplying by 1,000,000.

Demercuration (Sec 8.6): Use of sodium borohydride, NaBH₄ , to remove an acetoxymercury group and replace it with hydrogen.

DEPT (Sec 9.11D): A series of ¹³C NMR spectra in which the signal for each type of carbon, C, CH, CH₂ and CH₃, is printed out separately; data from DEPT spectra help identify the different types of carbon atoms in a ¹³C NMR spectrum. Also called distortionless enhanced polarization transfer spectroscopy

Desiccant (Lab 2.24): An agent that absorbs moisture; a drying agent.

Desiccate: To dry thoroughly; to render free from moisture.

Desiccator: An apparatus in which a substance is placed for drying, such as a chamber containing a desiccant.

Desulfonation (Sec 15.5): Replacement of the sulfonic acid group, -SO₃H, by a hydrogen; in benzene derivatives, this is done by heating with water or steam.

Dextrorotation (Sec 5.8B): (1) A turning or twisting to the right. (2) The clockwise turn given the plane of plane-polarized light by solutions of dextrorotatory optically active compounds.

Dextrorotatory (Sec 5.8B): An optically active compound that rotates plane-polarized light clockwise; designated d or (+).

Dialkyloxonium ion (Sec 3.12, 11.5, 11.12): A protonated ether, RO⁺(H)R' , with a positive charge on the oxygen atom, which is the conjugate acid of an ether, ROR'.

Diastereomers (Sec 5.2): Stereoisomers that are not mirror images of each other. Also called geometric isomers.

Diastereoselective reaction (Sec 5.10B, 12.3D): Production of a preponderance of one diastereomer over the other by a reaction where stereogenic centers are altered or created.

Diastereotopic hydrogen atoms (Sec 9.8B, Lab 8.3): When replacement of each of two hydrogen atoms by the same group yields compounds that are diastereomers, then the two hydrogen atoms have different chemical shifts, and give different ¹H NMR signals, although some peaks may be very close together or they may coincidentally overlap.

Diazo coupling (Sec 20.8): The use of an electrophilic diazonium salt in electrophilic aromatic substitution, such as the reaction of an aryl diazonium salt with an arene, which forms a compound of the type ArN=NAr'. The arene must be strongly activated toward electrophilic aromatic substitution; that is, it must bear a powerful electron-releasing substituent such as -OH or -NR₂ .

Diazonium ion (Sec 20.6): Ion of the type R-N⁺≡N: Aryl diazonium ions are formed by treatment of primary aromatic amines with nitrous acid, HNO₂ , which can be used to prepare aryl halides, phenols, and aryl cyanides, or to deaminate the amine.

Diazotization of an amine (Sec 20.6, 20.7, 21.4A): The reaction of a primary aromatic amine with nitrous acid, HNO₂ , which forms a diazonium ion, R-N⁺≡N: and can be used to prepare aryl halides, phenols, and aryl cyanides, or to deaminate the amine.

Dicarboxylic acid (Sec 17.2D): Compound with two carboxyl groups, -COOH. Also called alkanedioic acid.

Dieckmann condensation (Sec 19.2): An intramolecular Claisen condensation that forms a five- or six-membered ring, which is a base-catalyzed cyclization of a dicarboxylic acid ester to produce a cyclic β-ketoester. Also called Dieckmann reaction or Dieckmann cyclization.

Dielectric constant (ε or κ) (Sec 6.13C, Lab 3.2): (1) The increase in capacitance, equal to ε, that is created when a substance fills the space between the plates of a capacitor. (2) A measure of the polarity of a molecule, and the ability to insulate opposite charges from each other; a vacuum has ε = 1, molecules with 1 < ε < 3 are nonpolar, molecules with 3 ≤ ε < 10 are slightly polar, molecules with 10 ≤ ε < 20 are moderately polar, and molecules with ε ≥ 20 are very polar.

Diels-Alder reaction (Sec 13.10): A cycloaddition reaction between a conjugated diene and a substituted alkene (dienophile) to form a substituted cyclohexene product (adduct); four pi electrons in the diene interact with two pi electrons in the dienophile to form two new sigma bonds and the loss of two pi bonds, such that up to four new stereogenic centers may be created simultaneously.

Diene (Sec 13.5, 13.10): (1) An alkene with two carbon-carbon double bonds; also called an alkadiene. (2) The component with four pi electrons, usually two conjugated C=C double bonds, that reacts with a dienophile in a Diels-Alder reaction.

Dienophile (Sec 13.10): The component with two pi electrons, usually one C=C double bond, that reacts with a diene in a Diels-Alder reaction.

Dihedral angle (Sec 4.8, 9.9D): The angle that is formed whenever two planes meet.

Dimer: Molecule formed by the combination of two identical molecules.

Diol (Sec 11.2, 11.3C): A compound with two alcohol functional groups. Also called glycol.

Dipolar ion (Sec 24.2C): The charge-separated form of an amino acid that results from the transfer of a proton from a carboxyl group to a basic group.

Dipole moment (μ) (Sec 2.2): A measure of the degree of charge separation in a molecule, which is the product of the positive charge, Q, in electrostatic units (esu) and the distance, d, that separates them, in centimeters: μ = Q ∙ d, with units in debyes, D, where 1 D = 1 x 10^-18 esu ∙ cm = 3.336 x 10^-30 C ∙ m (coulomb meter). The larger the dipole moment, the more polar the molecule.

Dipole-dipole forces (Sec 2.13B): Weak forces between molecules that have permanent dipole moments, due to attraction of the charged end of one dipole to the oppositely charged end of an adjacent dipole; often allows solvation of polar molecules in a polar solvent.

Dipole-induced dipole forces (Sec 2.13): Weak attractive forces between a polar molecule and a nonpolar molecule, which are produced when the charged end of the permanent dipole induces a temporary polarity of opposite charge in the nonpolar molecule.

Direct alkylation of esters (Sec 18.4C): An alkylation reaction involving the conversion of an ester into its enolate with LDA (lithium diisopropylamide), followed by an S_N2 reaction with a primary alkyl halide.

Direct alkylation of ketones (Sec 18.4B): An alkylation reaction involving the conversion of a ketone into its enolate with LDA (lithium diisopropylamide), followed by an S_N2 reaction with a primary alkyl halide.

Directed aldol reaction (Sec 19.5B): A crossed aldol reaction is forced to occur between a ketone enolate and an aldehyde by first deprotonating the ketone with LDA (lithium diisopropylamide), then slowly adding the aldehyde; if the ketone is unsymmetrical, then it will be selectively deprotonated by LDA at the less substituted α carbon to form the kinetic enolate.

Disaccharide (Sec 22.1A): A carbohydrate undergoes hydrolytic cleavage to yield two molecules of a monosaccharide.

Dispersion forces (Sec 2.13B, 4.12B): Weak attractive forces between induced dipoles that exist between all molecules, that are produced when a temporary unsymmetrical electron distribution produces a temporary polarity in an atom, which induces a temporary polarity of opposite charge in an adjacent atom. The strength of London dispersion force increases with increasing polarizability of the atoms and increasing surface area of the molecule. Also called London forces, or London dispersion forces.

Distortionless Enhanced Polarization Transfer Spectroscopy (Sec 9.11D): A series of ¹³C NMR spectra in which the signal for each type of carbon, C, CH, CH₂ and CH₃ , is printed out separately; data from DEPT spectra help identify the different types of carbon atoms in a ¹³C NMR spectrum. Also called DEPT.

Distribution coefficient (Lab 5.3): A quantitative expression, K, for the amount of a substance, A, that dissolves in two separate immiscible solvents, where K is equal to the solubility of A in g/ml in the extracting solvent, Sx, divided by the solubility of A in the original solvent, So. Also called the partition coefficient.

Disulfide (Sec 24.2): A compound of the type RSSR'.

Disulfide bridge (Sec 24.2): An S-S bond between the sulfur atoms of two cysteine residues in a peptide or protein. Also called a disulfide linkage.

Dithiane (Sec 19.7): A thioacetal of formaldehyde that is sufficiently acidic to be deprotonated by exceptionally strong bases. Also called a 1,3-dithiane.

DNA (deoxyribonucleic acid) (Sec 25.1): A polynucleotide of 2'-deoxyribose present in the nuclei of cells that serves to store and replicate genetic information. Genes are DNA.

Double bond (Sec 1.4A, 1.13A): Chemical bond formed when two atoms share two pairs of electrons by forming one sigma bond and one pi bond.

Downfield (Sec 9.3, Lab 8.3): The left side of a NMR spectrum where deshielded nuclei absorb, at larger delta values, and at higher radio frequencies (or lower external magnetic fields, which is "down the field").

E

E-Z system (Sec 7.2): System for specifying double-bond configuration that is an alternative to cis-trans notation. Rank is determined by the Cahn-Ingold-Prelog system. When higher ranked substituents are on the same side of the double bond, the configuration is Z. When higher ranked substituents are on opposite sides, the configuration is E.

E1 reaction (Sec 6.15C, 6.17, 6.18B, 7.7): A unimolecular β elimination in which, in a slow rate-determining step, a leaving group departs from the substrate to form a carbocation, then in a fast step, the carbocation loses a proton to form a pi bond.

E2 reaction (Sec 6.15C, 6.16, 6.18A, 7.6): A bimolecular β elimination in which, in a single step, a base removes a proton, while a leaving group departs from the substrate, resulting in the formation of a pi bond.

Eclipsed conformation (Sec 4.8): A conformation of a molecule in which the relative position of any two substituents on adjacent atoms directly oppose each other, with a dihedral angle between their bonds of 0°.

Edman Degradation (Sec 24.5): Method for determining the N-terminal amino acid of a peptide or protein. It involes cyclic degradation of peptides based on the reaction of phenylisothiocyanate with the free amino group of the N-terminal residue such that amino acids are removed one at a time and identified as their phenylthiohydantoin derivatives.

Electromagnetic radiation (Sec 2.15, 9.2, 13.9, Lab 8): Various forms of electromagnetic waves that propagate at the speed of light; includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Electromagnetic spectrum (Sec 2.15, 9.2, 13.8, Lab 8): The full range of electromagnetic frequencies from radio waves to gamma rays.

Electron affinity: Energy change associated with the capture of an electron by an atom.

Electron density surface (Sec 1.12): Structure that shows a calculated 3-D surface with the same electron density everywhere on that surface.

Electronegativity (Sec 1.3A, 2.2): A measure of the ability of an atom to attract shared electrons to itself, and thereby polarize a covalent bond.

Electron impact ionization (Sec 9.14, 9.16A): An ionization method in mass spectrometry that places a sample under high vacuum then bombards it with a beam of high-energy electrons, which dislodges a valence electron from the gas-phase molecules and produces molecular ions that have a +1 charge and an unshared electron. Also called EI ionization.

Electron probability density (Sec 1.10): The probability of finding an electron in a given region of space, which is given by the square of the wave function, ψ².

Electron-releasing group (Sec 6.11B, 15.11): An atom or group that increases the electron density around another atom by an inductive or resonance effect.

Electron-withdrawing group (Sec 15.11): An atom or group that decreases the electron density around another atom by an inductive or resonance effect.

Electrophile (Sec 3.4A, 8.1, Lab 15.1): An "electron-loving" species; a cation or electron deficient molecule (with a δ+ charge, or an empty p orbital) that can accept a pair of electrons to form a new covalent bond; electrophiles include Brønsted-Lowry acids (proton donors) such as HBr, H₂SO₄ , etc., Lewis acids (electron-pair acceptor) such as BH₃ , BF₃ , AlCl₃ , FeCl₃ , ZnCl₂ , etc., metal ions with vacant orbitals such as Ag⁺, Hg²⁺, Pt²⁺, etc., and neutral molecules with large polarizable atoms such as Br₂ , I₂ , etc.

Electrophilic addition (Sec 8.1 - 8.5, 13.10): An addition reaction in which a polarizable reagent, E-N, is attacked by the pi electrons of an alkene (or alkyne) on the electrophilic portion (E), which initially forms a carbocation intermediate that is subsequently attacked by the nucleophilic portion (N) of the reagent; the product contains E attached to one carbon and N attached to the adjacent carbon. Also called ionic addition reaction.

Electrophilic aromatic substitution (Sec 15.1, 21.8, Lab 15.1): Replacement of a hydrogen on an aromatic ring by a strong electrophile. Also called S_E2 reaction for Substitution, Electrophilic, Bimolecular.

Electrophoresis (Sec 25.6A): A technique for separating charged molecules based on their different mobilities in an electric field.

Electrospray ionization (Sec 9.19): An ionization method in mass spectrometry in which a solution of the analyte is sprayed into the vacuum chamber of the MS from the tip of a high-voltage needle, and the extreme electrical potential imparts multiple charges to the analyte, and thus a family of m/z peaks. Also called ESI.

Electrostatic attraction: Force of attraction between oppositely charged particles.

Electrostatic potential map (Sec 1.8, 2.2A): Computer generated structure that uses color to show the relative distribution of electron density at the Van der Waals surface of a molecule or ion; violet shows electron-poor regions that have a positive charge (+); blue to blue-green show regions that have a partial positive charge (δ+); green shows regions of normal electron density with no charge (0); yellow to orange show regions that have a partial negative charge (δ─); red shows electron-rich regions that have a negative charge (─). Also called map of electrostatic potential.

Element (Sec 1.2): Fundamental form of matter composed of atoms of only one kind (identical atomic number), that cannot be broken apart into a different form of matter by ordinary physical or chemical means.

Elimination reaction (Sec 3.1, 6.15 - 6.17, 7.5 - 7.7): A reaction that results in the loss of two groups from a substrate, with the formation of a pi bond. The most common elimination is a β elimination (1,2 elimination), in which the two groups are lost from adjacent atoms.

Elimination-addition mechanism (Sec 21.11B): Two-stage mechanism for a type of nucleophilic aromatic substitution reaction; in the first stage, an aromatic halide undergoes elimination to form a benzyne intermediate, then in the second stage, nucleophilic addition to the benzyne yields the product of the reaction.

Eluant (Lab 6.3): (1) A solvent or solution used in an elution process. (2) The mobile phase in chromatography. Also called eluent, or eluting solvent, or developer.

Eluate (Lab 6.3): (1) The solution of solvent and dissolved matter resulting from elution. (2) The solution emerging from a chromatographic column that has removed the sample components from the stationary phase.

Eluent (Lab 6.3): (1) A solvent or solution used in an elution process. (2) The mobile phase in chromatography. Also called elutant, or eluting solvent, or developer.

Elution (Lab 6.3): (1) The removal by means of a suitable solvent of one material from another in column chromatography. (2) The separation by washing of one solid from another.

Empirical formula: A reduced molecular formula that expresses the kinds of atoms and the relative proportions of elements in a compound as the smallest set of whole numbers, which is the simplest ratio of elements.

Enal (Sec 19.4C): An alkene aldehyde, which is usually conjugated, such as an α,β-unsaturated aldehyde, R₂C=CHCHO.

Enamine (Sec 16.8, 18.9, 19.7A): A vinyl amine, usually generated by the acid-catalyzed reaction of a secondary amine with an aldehyde or ketone, which has the general formula: R₂C=C(NR₂)R.

Enantiomeric excess (Sec 5.9B): A measure of the percentage optical purity, or enantiomeric purity; calculated for a mixture of enantiomers by dividing the difference of moles of the two enantiomers by the total moles of both enantiomers, then multiplying by 100%.

Enantiomeric purity (Sec 5.9B): A measure of the enantiomeric excess; calculated for a mixture of enantiomers by dividing the difference of moles of the two enantiomers by the total moles of both enantiomers, then multiplying by 100%.

Enantiomers (Sec 5.2, 5.3, 5.7, 5.8): Stereoisomers that are nonsuperposable mirror images of each other.

Enantioselective reaction (Sec 5.10B, 12.3): Production of a preponderance of one enantiomer over the other by a reaction where chirality centers are altered or created.

Enantiotopic hydrogen atoms (Sec 9.8B, Lab 8.3): When replacement of each of two hydrogen atoms by the same group yields compounds that are enantiomers, then the two hydrogen atoms have the same chemical shift, and give only one ¹H NMR signal.

Endergonic reaction (Sec 6.7): A reaction that absorbs energy, and has a positive ΔG. (Origin: end = within; ergon = work)

Endo group (Sec 13.10): In a bridged ring system, the isomer with the substituent located syn, or closest to the longest bridge.

Endothermic reaction (Sec 3.8-3.9, 6.7): A reaction that absorbs heat, and has a positive ΔH. (Origin: endo = within; therm = heat)

Energy (Sec 3.8): The capacity to move matter and do work, or to transfer heat.

Energy of activation, E_act (Sec 10.5A): The difference in enthalpy, ΔH, of the transition state and the reactants; for reactions with very small entropy changes, ΔS ≈ 0 and ΔG ≈ ΔH, so the energy of activation is almost the same as the free energy of activation ( E_act ≈ ΔG^‡ ). Also called activation energy.

Enol (Sec 18.1 - 18.3, Lab 18.1): An alkene alcohol that is formed by tautomerization of an aldehyde or ketone, which has the general formula: R₂C=C(OH)R'.

Enolate anion (Sec 18.1 - 18.7, Lab 18.1): The resonance-stabilized anion formed by deprotonating the α carbon atom adjacent to a carbonyl group, or by deprotonating the hydroxyl group of an enol tautomer.

Enolizable hydrogen (Sec 18.1): An α-hydrogen that is lost and regained through keto-enol tautomerization, thus losing its stereochemistry in the process.

Enone (Sec 19.4C): An alkene ketone, which is usually conjugated, such as an α,β-unsaturated ketone, R₂C=CHCOR.

Enthalpy, H (Sec 3.8-3.9): The heat content of a system, defined as: H = E + PV, where E is the internal energy of the system, P is the pressure, and V is the volume.

Enthalpy change, ΔH (Sec 3.8-3.9): The heat of reaction, which measures the amount of heat released or absorbed by a system

Entropy, S (Sec 3.8-3.9): (1) A measure of the degree of disorder of a system. (2) The part of the energy of a system which is not available to perform useful work.

Entropy change, ΔS (Sec 3.8-3.9): The change in the relative order of a system; a reaction that increases the disorder of a system has a positive ΔS; total entropy increases in all spontaneous natural processes.

Epimerization (Sec 18.3A): Conversion of a less stable epimer to a more stable epimer by keto-enol tautomerization.

Epimers (Sec 18.3A): Diastereomers that differ in configuration at only one chirality (stereogenic) center.

Epoxidation (Sec 11.13A): Reaction of an alkene with a peroxy acid, RCO₃H, to form an epoxide; common peroxy acids are MCPBA (meta-chloroperoxybenzoic acid) and MMPP (magnesium monoperoxyphthalate).

Epoxide (Sec 11.13, 11.14): A cyclic ether with a three-membered ring, containing one oxygen and two carbon atoms. Also called an oxirane.

Equatorial bond (Sec 4.12): The six bonds of a cyclohexane ring that extend from the perimeter of the ring, and that alternate slightly up and slightly down at an angle of about 20° to the average plane of the ring.

Equilibrium constant, K_eq (Sec 3.5A): A constant that expresses the position of an equilibrium, which is calculated by multiplying the molar concentrations of the products, each raised to the power of its coefficient, and dividing by the molar concentrations of the reactants, each raised to the power of its coefficient; for the general chemical equation: aA + bB ↔ cC + dD , the equilibrium constant is: K_eq = [C]^c [D]^d / [A]^a [B]^b

Equilibrium control (Sec 13.10A): A principle stating that the ratio of products of a reaction that reaches equilibrium is determined by the relative stabilities of the products (as measured by their standard free energies, ΔG°). The most abundant product will be the one that is the most stable. Also called thermodynamic control.

Equilibrium vapor pressure (Lab 4.2): The magnitude of the vapor pressure, at a given temperature, for a liquid that is in a state of dynamic equilibrium with its gas phase.

Essential oil (Sec 23.3): A volatile odoriferous compound obtained by steam distillation of plant material.

Ester (Sec 2.10B, 17.2E, Lab 20.2): A molecule containing a carbonyl group, >C=O , that is attached to an alcohol group, -OR' , with the general formula RCOOR' , often formed by the reaction of a carboxylic acid and an alcohol with loss of water. Also called carboxylic ester.

Ether (Sec 2.7, 11.1, 11.11): Molecule containing an oxygen atom bonded to two alkyl or aryl groups, with the general formula ROR'.

Ethyl group (Sec 4.3): The alkyl group CH₃CH₂-.

Eutectic mixture (Lab 3.3): A mixture of two substances in which the melting point of the mix is lower than the melting point of either of the components.

Eutectic point (Lab 3.3): The lowest possible melting point of a mixture of two substances.

Eutectic temperature (Lab 3.3): The temperature at which a eutectic mixture becomes fluid and melts.

Exchangeable protons (Sec 9.10): The hydrogens (protons) attached to oxygen or nitrogen can be rapidly exchanged between molecules. Addition of heavy water (D₂O, deuterium oxide) will allow exchange between these hydrogens and deuterium, and the ¹H NMR signal will disappear, or be reduced in height, because deuterium does not produce a signal in ¹H NMR.

Exergonic reaction (Sec 6.7): A reaction that releases energy, and has a negative ΔG. (Origin: ex = external; ergon = work)

Exo group (Sec 13.10): In a bridged ring system, the isomer with the substituent located anti, or furthest from the longest bridge.

Exothermic reaction (Sec 3.8-3.9, 6.7): A reaction that releases heat, and has a negative ΔH. (Origin: exo = external; therm = heat).

Extinction coefficient, ε (Sec 13.8, Lab 8.4): The proportionality constant that relates the concentration of a compound to its absorbance of light, as defined by the Beer-Lambert Law: ε = A / ( c ∙ l ), where A is the absorbance at a particular wavelength, c is the concentration, and l is the path length in cm of the light beam through the sample cell. Also called molar absorptivity when units are M^-1 cm^-1 .

F

Faraday's Law of Induction: The induced electromotive force (EMF) in any closed circuit is proportional to the rate of change of the magnetic flux through the circuit.

Fat (Sec 23.2): A triacylglycerol. The triester of glycerol with 3 carboxylic acids.

Fatty acid (Sec 23.2): A long-chained linear carboxylic acid (usually with an even number of carbon atoms) that is isolated by the hydrolysis of a fat.

Filtrate (Lab 3.2): Solution that passes through the filter paper.

Filter-aid (Lab 3.2): Insoluble forms of silicon dioxide, such as Celite, that assist filtration by adsorption of particles.

Fingerprint region of IR (Sec 2.16, Lab 8.2): The right one-third of an infrared spectrum, in the region 1400 - 400 cm^-1 of an infrared spectrum, where most of the bending vibrations and many complex vibrations occur; no two different compounds (except enantiomers) have exactly the same absorptions in this region.

Fischer esterification (Sec 17.7A): The acid-catalyzed reaction of a carboxylic acid with an alcohol to give a carboxylic ester and water.

Fischer projection formula (Sec 5.13, 22.2C): A two-dimensional formula for representing the configuration of a chiral molecule; written with the main carbon chain extending from top to bottom with all groups eclipsed; vertical lines represent bonds that project behind the plane of the page (or that lie in it); horizontal lines represent bonds that project out of the plane of the page.

Fixed-thickness cell (Lab 8.2): A sample cell used in IR spectroscopy that is constructed of two transparent salt plates separated by a gasket, which defines the thickness of the sample contained in the cell.

Flame emission spectrophotometry: Determination of the concentration of an element by measurement of light emitted when the element is excited by energy in the form of heat.

Fluorination (Sec 10.5C): A reaction in which fluorine atoms are introduced into a molecule.

Formal charge (Sec 1.5): The charge on an atom in a molecule or ion, which is determined as the difference between the number of electrons assigned to an atom in a molecule and the number of electrons it has in its outer shell in its elemental state. The formal charge on an atom can be calculated using the formula: F = Z ─ S/2 ─ U, where F is the formal charge, Z is the group number of the atom (i.e., the number of electrons the atom has in its outer shell in its elemental state), S equals the number of electrons the atom is sharing with other atoms, and U is the number of unshared electrons (lone pair electrons) that the atom possesses.

Formyl group (Sec 16.2): The -CHO group. Also called a methanoyl group.

Fourier transform infrared spectrometer (FT–IR) (Sec 2.15, Lab 8): An instrument that passes infrared light through both the sample and a scanning interferometer to give an interference pattern (interferogram), which is digitized, and the Fourier transformed spectrum is calculated.

Fractional distillation (Lab 4.4): A method that allows separation of several volatile substances whose boiling points do not differ greatly, and uses a fractional distillation column between the stillpot and stillhead.

Fragmentation pattern (Sec 9.16): Ions produced by dissociation of the molecular ion in mass spectrometry.

Free energy change, ΔG (Sec 3.9, 6.7): A measure of the amount of free energy of a system (energy available to do work); defined as: ΔG = ΔH - T ΔS, where ΔH is the enthalpy change, T is the absolute temperature, and ΔS is the entropy change. The relation between the standard Gibbs free energy change, ΔG°, and the equilibrium constant, K_eq , is defined as: ΔG° = ─ R T ln( K_eq ), where R is the gas constant ( 8.314 J/mol ∙ K ), and ln( ) is the natural logarithm function. Also called Gibbs free energy change.

Free energy diagram (Sec 6.7): A plot of the energy of the reacting particles (y-axis) versus the reaction coordinate (x-axis); it displays Gibbs free energy changes, ΔG, as a function of the progress along a reaction pathway that must take place as reactants are converted into products.

Free energy of activation, ΔG^‡ (Sec 6.7): The difference in Gibbs free energy, ΔG, of the transition state and the reactants; the smaller the free energy of activation, the faster the rate of reaction.

Freon (Sec 10.12D): A chlorofluorocarbon (CFC), such as CFCl₃ or CF₂Cl₂ .

Free radical (Sec 3.1A, 10.1, 10.6, 10.7): An uncharged electron deficient chemical species with an odd number of valence electrons due to an orbital with an unpaired electron; examples include the chlorine radical atom, Cl∙ , the tert-butyl radical, (CH₃)₃ C∙ , etc. Also called a free radical.

Free-radical polymerization (Sec 10.10): An alkene polymerization proceeding via free-radical intermediates. Also called radical polymerization.

Frequency, υ (Sec 2.15, 9.2, 13.8, Lab 8): The number of complete wave cycles that pass a fixed point in a second, or the number of reversals of the electromagnetic field per second; usually expressed in Hertz (Hz), which is cycles per second (cps or s^-1 ).

Friedel-Crafts acylation (Sec 15.7, Lab 15.3): Formation of an acyl arene (alkyl aryl ketone), Ar-C(=O)R, by replacement of an aromatic ring hydrogen atom with an acyl group via an acylium ion intermediate.

Friedel-Crafts alkylation (Sec 15.6, Lab 15.2): Formation of an alkyl arene, Ar-R, by replacement of an aromatic ring hydrogen atom with an alkyl group via a carbocation intermediate.

Fries rearrangement: Aluminum chloride-promoted rearrangement of an aryl ester to a ring-acylated derivative of phenol.

Fullerene (Section 14.8C): A class of aromatic compounds with an even number of carbon atoms, which form a cage-like fused-ring polycyclic system with twelve five-membered rings and the rest six-membered rings. For example, [60]fullerene has the geometry of a truncated icosahedron and is called buckminsterfullerene.

Functional class nomenclature (Sec 4.3E): A system for naming compounds that uses two or more words to describe the compound. The final word corresponds to the functional group present; the preceding words, usually listed in alphabetical order, describe the remainder of the molecule, i.e., methyl alcohol, ethyl methyl ether, ethyl bromide.

Functional group (Sec 2.4): The particular group of atoms in a molecule that determines how the molecule reacts by giving predictable properties and reactivity to the molecule.

Functional group interconversion (Sec 6.14): A process that converts one functional group into another.

Functional group region of IR (Sec 2.16, Lab 8.2): The left two-thirds of an infrared spectrum, in the region 4000 - 1400 cm^-1, where most of the functional groups undergo stretching vibrations and produce reliable absorptions in this region.

Furanose (Sec 22.2C): A sugar in which the cyclic acetal or hemiacetal ring is five membered.

G

Gabriel amine synthesis (Sec 20.4A): Synthesis of primary amines by alkylation of the potassium salt of phthalimide, followed by displacement of the amine by hydrazine.

Gatterman-Koch synthesis: The synthesis of benzaldehydes by treating a benzene derivative with CO and HCl using an AlCl₃ / CuCl catalyst.

Gauche conformation (Sec 4.9): A staggered conformation of a molecule in which the two largest substituents on adjacent atoms are a small distance apart, with a dihedral angle between their bonds of 60°.

GC / MS analysis (Sec 9.18): A technique that couples gas chromatography (GC) with mass spectrometry (MS); the GC separates components of a mixture, then the MS gives the molecular weight and structural information about each component.

Geminal (gem-) (Sec 7.10): Substituents that are on the same atom.

Gibbs free energy change, ΔG (Sec 3.9, 6.7): A measure of the amount of free energy of a system (energy available to do work); defined as: ΔG = ΔH - T ΔS, where ΔH is the enthalpy change, T is the absolute temperature, and ΔS is the entropy change. The relation between the standard Gibbs free energy change, ΔG°, and the equilibrium constant, K_eq , is defined as: ΔG° = ─ R T ln( K_eq ), where R is the gas constant ( 8.314 J/mol ∙ K ), and ln( ) is the natural logarithm function.

Glycogen (Sec 22.13B): A polysaccharide present in animals that is derived from glucose. Similar in structure to amylopectin.

Glycol (Sec 4.3F, 8.15, 11.2, 11.3C): A compound with two alcohol functional groups. Also called diol.

Glycolysis: Biochemical process in which glucose is converted to pyruvate with release of energy.

Glycoside (Sec 22.4): A cyclic mixed acetal of a sugar with an alcohol.

Grain alcohol (Sec 11.3B): A common name for ethanol (CH3CH2OH).

Grignard reagent (Sec 12.6-12.8): An organomagnesium halide, RMgX, which is a common source of carbanions; it is formed by the reaction of magnesium with an alkyl halide or aryl halide.

Ground state (Sec 1.12): The lowest electronic energy state of an atom or molecule.

H

Haloalkane (Sec 2.5, 6.1): Compound in which a halogen atom (F, Cl, Br, I) replaces a hydrogen atom of an alkane, with the general formula RX. Also called alkyl halide.

Haloform (Sec 18.3C): Compound formed by replacing three hydrogen atoms in methane, CH₄ , with halogen atoms to form CHX₃ .

Haloform reaction (Sec 18.3C): The reaction of a methyl ketone with a halogen and base to produce a carboxylate ion, RCOO‾, and a haloform, CHX₃ .

Halogenation (Sec 10.3 - 10.5, 10.8, 15.3): Incorporation of one or more halogen atoms into a molecule.

Halogen addition to alkenes (8.11): The electrophilic addition of two halogen atoms to each doubly bonded carbon atom in alkenes to produce a vic-dibromides, with anti stereochemistry.

Halogen addition to alkenes (8.11): The electrophilic anti addition of halogen atoms to each doubly bonded carbon atom in alkenes, through bridged halonium ion intermediates, to produce vic-dibromides.

Halonium ion (Sec 8.l1A): A species that incorporates a positively charged halogen; the positive charge may be delocalized onto the halogen through resonance; bridged halonium ions are intermediates in the addition of halogens to the double bond of an alkene.

Hammond-Leffler Postulate (Sec 6.l3A, 15.11): In a multistep reaction, the structure of a transition state of a given step will resemble the stable species that is nearest to it in free energy; the transition state of an endergonic step will resemble the products of that step, whereas the transition state of an exergonic step will resemble the reactants of that step.

Haworth formulas (Sec 22.2C): Planar representations of furanose and pyranose forms of carbohydrates.

Head Temperature (Lab 4.3): The temperature read on the thermometer in the stillhead in a distillation apparatus.

Heat of combustion (Sec 4.10A): The standard enthalpy change, ΔH°, for the complete combustion of one mole of a compound.

Heat of formation: The standard enthalpy change, ΔH°, for the formation of a substance from its elements.

Heat of hydrogenation (Sec 7.3A): The standard enthalpy change that accompanies the hydrogenation of one mole of an unsaturated compound.

HECTOR (Sec 9.12): A 2D NMR technique that correlates the ¹H chemical shift of a proton to the ¹³C chemical shift of the carbon to which it is attached. Also called heteronuclear correlation spectroscopy

Height Equivalent to a Theoretical Plate (HETP) (Lab 4.4): An index of the separating efficiency of a fractional distillation column, defined as the vertical length of a column that is necessary to obtain a separation efficiency of one theoretical plate.

Heisenberg uncertainty principle (Sec 1.11): Both the position and momentum of an electron (or any small object) cannot be exactly measured simultaneously.

Hell–Volhard–Zelinski Reaction (Sec 18.3D): Alpha-Halogenation of a carboxylic acid in the presence of catalytic phosphorus, to give an α-halo carboxylic acid; the reaction initially forms an acyl halide, which is in equilibrium with the enol form that undergoes alpha substitution with the halide, then the α-halo acyl halide is hydrolyzed with water to the α-halo carboxylic acid.

Hemiacetal (Sec 16.7A, 22.2C): The product of the nucleophilic addition of one molecule of an alcohol to an aldehyde or ketone; the hemiacetal has one alkoxy group, -OR, and one hydroxyl group, -OH, on the former carbonyl carbon atom. This derivative of a ketone is also called a hemiketal.

Hemiketal (Sec 16.7A): A hemiacetal derived from a ketone.

Henderson-Hasselbalch equation (Sec 24.2C): Relates the pH of a buffer to the degree of dissociation of a weak acid into hydrogen ion and its conjugate base, HA ↔ H ⁺ + A^‾ , using the math equation: pH = pKa + log( [conjugate base] / [acid] ).

Hertz, Hz (Sec 2.15, 9.6A, 9.9C, 13.8A, Lab 8): A measure of the frequency of a wave in cycles per second (cps or s^-1 ).

Hess's Law: For a chemical equation that can be written as the sum of two or more steps, the enthalpy changes, ΔH, for the overall equation equals the sum of the enthalpy changes for the individual steps.

Heteroatoms (Sec 2.1): Atoms in an organic compound that are not carbon or hydrogen, but they form covalent bonds and have lone pairs of electrons.

Heterocyclic compound (Sec 14.9): A cyclic compound that has an element other than carbon in the ring.

Heterocyclic aromatic compound (Sec 14.9): An aromatic cyclic compound that contains an element other than carbon, such as N, O, or S; examples include pyridine, C₅H₅N, pyrrole, C₄H₅N, furan, C₄H₄O, and thiophene, C₄H₄S.

Heterogeneous catalyst (Sec 7.12, 7.14A): Reactions where the catalyst is insoluble in the solvent in which the reaction is carried out.

Heterogeneous hydrogenation (Sec 7.13, 7.14): Hydrogenation of a multiple bond, that is catalyzed by a finely divided metal which is insoluble in the reaction mixture, such as platinum, palladium, nickel, rhodium, or ruthenium.

Heterogeneous reaction: A reaction involving two or more substances present in different phases.

Heterolysis (Sec 3.4): The cleavage of a polar covalent bond so that one fragment departs with both of the electrons of the bond that joined them, which usually produces both positive and negative ions. Also called heterolytic cleavage.

Heteronuclear Correlation Spectroscopy (Sec 9.12): A 2D NMR technique that correlates the ¹H chemical shift of a proton to the ¹³C chemical shift of the carbon to which it is attached. Also called HETCOR.

Heterotopic hydrogen atoms (Sec 9.8A, Lab 8.3): Hydrogen atoms that have different molecular connectivities are chemically nonequivalent, have different chemical shifts, and give different ¹H NMR signals, although some peaks may coincidentally overlap.

Hexose (Sec 22.2): A carbohydrate with six carbon atoms.

High-density lipoprotein (HDL): A protein that carries cholesterol from the tissues to the liver where it is metabolized; HDL is often called "good cholesterol."

Hinsberg test (Sec 20.9A, Lab 25.14A): The reaction of an amine with benzenesulfonyl chloride to form a benzenesulfonamide, in order to determine whether it is a primary, secondary, or tertiary amine.

Histones: Proteins that are associated with DNA in nucleosomes.

Hofmann elimination (Sec 20.12A): Elimination of a quaternary ammonium hydroxide by pyrolysis into an alkene and a tertiary amine, which usually gives the least-substituted alkene (Hofmann product). Also called Hofmann degradation.

Hofmann rearrangement (Sec 20.4E): Conversion of a primary carboxylic amide to a primary amine, with one fewer carbon atom, by treatment with bromine in aqueous NaOH, via an isocyanate intermediate. Also called Hofmann reaction.

Hofmann rule (Sec 7.6C, 20.12A). The major product of an elimination reaction that uses a bulky, strong base will be the less stable alkene, which has the less substituted double bond.

HOMO (Sec 3.3A, 6.6, 13.8C): The highest occupied molecular orbital; when a molecule in the ground state is excited, an electron may jump from a HOMO into a LUMO.

Homogeneous catalyst (Sec 7.12): Reactions where the catalyst is soluble in the solvent in which the reaction is carried out.

Homogeneous hydrogenation (Sec 7.12): Hydrogenation of a multiple bond, that is catalyzed by an organometallic compound which is soluble in the reaction mixture, such as complexes of rhodium or ruthenium with ligands.

Homologous series (Sec 4.7): A series of compounds in which each member differs from the next member by a constant unit.

Homolysis (Sec 10.1): The cleavage of a covalent bond so that each fragment departs with one of the electrons of the bond that joined them, which usually produces radicals. Also called homolytic cleavage.

Homolytic bond dissociation energy, DH (Sec 10.2): The enthalpy change that accompanies the homolytic cleavage of a covalent bond to produce two radicals: A-B → A∙ + B∙ , ΔH° = DH. Also called bond dissociation enthalpy.

Homotopic hydrogen atoms (Sec 9.8A, Lab 8.3): When replacement of each of two hydrogen atoms by the same group yields compounds that are identical, then the two hydrogen atoms are chemically equivalent, have identical chemical shifts, and give only one ¹H NMR signal.

Hot filtration (Lab 3.2): Heating a mixture before and during filtration

Hückel's rule (Sec 14.7): A rule stating that planar monocyclic rings with (4n + 2) delocalized pi electrons will be aromatic; Hückel numbers include 2, 6, 10, 14, 18, 22, 26, 30, . . .

Hund's rule (Sec 1.10A): Orbitals in a subshell must all be half-filled before any can be completely filled with electrons; when orbitals are degenerate (of equal energy), then electrons with the same spin are added to each orbital until all degenerate orbitals contain one electron, and then electrons are added to each orbital so that the spins are paired.

Hybridization of atomic orbitals (Sec 1.12 - 1.15): A mathematical (and theoretical) mixing of two or more atomic orbitals to give the same number of new hybrid orbitals, each of which has some of the character of the original atomic orbitals.

Hydration (Sec 8.4 - 8.9, 11.4): The addition of the components of water, H₂O, to a molecule.

Hydrazone (Sec 16.8B): A compound containing the -C=N-NH₂ group, formed by the reaction of an aldehyde or ketone with hydrazine, NH₂ NH₂ .

Hydride ion (Sec 7.8, 12.1A, 12.3): A hydrogen atom that has two electrons and a negative charge, :H^- , which is a powerful nucleophile and a very strong base (pKa = 35); common sources of hydride ions are lithium aluminum hydride, LiAlH₄ , and sodium borohydride, NaBH₄ .

Hydride migration (Sec 7.8A): Migration of a hydride ion, :H^- , from a carbon adjacent to a carbocation, which usually forms a more stable carbocation. Also called hydride shift, or hydride rearrangement.

Hydroboration (Sec 8.6, 8.7, 11.4): The addition of a boron hydride (either BH₃ or an alkylborane) to a multiple bond.

Hydroboration-oxidation of alkenes (Sec 8.7, 8.8, 11.4): A two-step method that converts an alkene into an alcohol, with anti-Markovnikov regiochemistry, syn stereochemistry, and usually no rearrangements. The first step is hydroboration that adds borane, BH₃ , to the C=C group of an alkene. The second step is oxidation and hydrolysis of the alkylborane intermediate using basic hydrogen peroxide, H₂O₂ , to produce the less substituted alcohol.

Hydrocarbon (Sec 2.2): Molecule that contains only carbon and hydrogen atoms.

Hydrogen abstraction (Sec 10.1B): A reaction in which a radical removes a H∙ radical atom from a molecule that is converted into a new radical.

Hydrogen bond (Sec 2.13B): The strongest type of dipole-dipole force, which occurs between an O, N, or F atom, and a H atom that is bound to another O, N, or F atom; it often allows solvation of molecules in water.

Hydrogenation (Sec 4.16, 7.3A, 7.13 - 7.15, 12.2): (1) Reduction of a compound by adding a pair of hydrogen atoms, H∙ , or by adding both a hydride ion, :H^- , and a hydrogen ion, H⁺ . (2) An addition reaction in which hydrogen adds to a double or triple bond, which is often accomplished through the use of a metal catalyst, such as platinum, palladium, nickel, rhodium, or ruthenium.

Hydrohalogenation reaction (Sec 8.1 - 8.4): An electrophilic addition reaction of a hydrogen halide (HCl, HBr, etc.) to an alkene (or alkyne), which produces the corresponding haloalkane (alkyl halide).

Hydrolysis: Cleavage of a covalent bond by adding a molecule of water.

Hydronium ion: The species H₃O⁺ .

Hydrophilic group (Sec 2.13D, 11.2, 16.3, 17.2, 23.2, Lab 5.3): A polar (water-loving) group that seeks an aqueous environment.

Hydrophobic effect (Sec 2.13D, Lab 5.3): The excluding of nonpolar molecules from an aqueous solution.

Hydrophobic group (Sec 2.13D, 11.2, 16.3, 17.2, 23.2, Lab 5.3): A nonpolar (water-fearing) group that avoids an aqueous environment and seeks a nonpolar environment. Also called lipophilic.

Hydroxylamine (Lab 25.16A): The compound H₂NOH; or generically, an amine in which a hydroxyl group is one of the three substituents bonded to nitrogen.

Hydroxylation (Sec 8.16, 11.15): The addition of hydroxyl groups to each carbon or atom of a double bond.

Hygroscopic (Lab 8.2): A substance that readily absorbs and retains moisture.

Hyperconjugation (Sec 4.8, 6.11B, 10.2B): The phenomenon of electron delocalization, via orbital overlap from a filled bonding molecular orbital to an adjacent unfilled orbital, which stabilizes the molecule or ion.

I

Ideal Solution (Lab 4.3): A solution in which interactions between like molecules are the same as those between unlike molecules.

Imide (Sec 17.8C): A compound with two carbonyl groups bound to the same nitrogen atom, RCONHCOR'.

Imine (Sec 16.8A, 20.4C): A compound with a carbon-nitrogen double bond, R₂C=NR', formed by the reaction of a ketone or aldehyde with a primary amine; a substituted imine is often called a Schiff base.

Immiscible liquid phases (Lab 5.3): Liquids that are not soluble in each other, so they form separate layers when mixed, such as water and diethyl ether.

Index of hydrogen deficiency (IHD) (Sec 4.17): A measure of the total number of pi bonds and rings that a molecule contains, which equals the difference in the number of pairs of hydrogen atoms between the molecular formula for the compound under study (C_nH_x ), and the acyclic alkane having the same number of carbons ( C_nH_2n+2 ), according to the equation: IHD = (2n + 2 - x) / 2. For compounds containing halogens, replace each halogen atom with a hydrogen atom. For compounds containing oxygen, simply remove all oxygen atoms. For compounds containing nitrogen, delete one hydrogen atom for each nitrogen atom, then remove all nitrogen atoms. Also called degree of unsaturation, or double-bond equivalence.

Inductive effect (Sec 3.7B, 3.10B, 15.11B): Polarization of a molecule, due to the effect of a group that is either electron-donating or electron-withdrawing, which is transmitted through space and through the bonds of the molecule, but the effect gets weaker with increasing distance from the group.

Inductive stabilization (Sec 6.11B, 15.11B): Stabilization of a reactive intermediate by donation or withdrawal of electron density through sigma bonds; i.e., alkyl groups stabilize carbocations and arenium ions through hyperconjugation.

Infrared spectroscopy (Sec 2.15, Lab 8.2): A type of optical spectroscopy that measures the absorption of infrared radiation ( 4000 - 400 cm^-1, or 2.5 - 25 μm ), and it provides structural information about functional groups present in the compound being analyzed. Also called IR spectroscopy.

Inorganic esters: Compounds derived from alcohols and inorganic acids with loss of water, such as sulfate esters, sulfonate esters, nitrate esters, phosphate esters, etc.

Integration curve for NMR (Sec 9.2B, Lab 8.3): The areas under the peaks in a ¹H NMR spectrum that are calculated and plotted as a stepped trace that appears on the spectrum.

Interferometer (Sec 2.15): The light measuring portion of an FT–IR spectrometer. The light is split into two beams, and one beam is reflected from a stationary mirror, while the other beam is reflected from a moving mirror, then the beams are recombined to form an interference pattern, called an interferogram, then fourier transformation of the interferogram gives the spectrum.

Intermediate (Sec 6.10 - 6.11): A transient species that exists between reactants and products in a state corresponding to a local energy minimum between two transition states on a free energy diagram.

Intermolecular forces (Sec 2.13, 2.14): All of the noncovalent electrostatic forces of attraction or repulsion which act between neighboring molecules, groups and atoms, which include the forces of ions, dipoles and electron clouds; these forces determine many physical properties of the molecules, such as melting point, boiling point and solubility. In biochemistry, intermolecular forces also include the ionic forces of molecular ions, such as proteins, nucleic acids, phospholipids, etc.

Inversion of configuration (Sec 6.6, 6.8): A change of configuration, such as from R to S, or from cis to trans, or vice versa, that occurs when a nucleophile attacks a stereogenic carbon from its back-side in an S_N2 reaction. Also called Walden inversion.

Iodination (Sec 10.5C): A reaction in which one or more iodine atoms are introduced into a molecule.

Iodoform (Sec 17.3C): Compound formed by replacing three hydrogen atoms in methane, CH₄ , with iodine atoms to form CHI₃ .

Iodoform test (Sec 18.3C): A chemical test for methyl ketones, which react with iodine, I₂ , and base (usually aqueous NaOH) to produce a precipitate of iodoform, CHI₃ , which is a yellow solid.

Ion (Sec 1.3A, 3.1A): A chemical species that bears an electrical charge.

Ion sorting (Sec 9.18B): The method used in mass spectrometry to separate the ions of the sample that have been formed prior to detection.

Ion-dipole forces (Sec 2.13D): Moderate strength electrostatic forces between an ion and the oppositely charged end of a permanent dipole; often allows solvation of ions in a polar solvent.

Ion-ion forces (Sec 2.13A): Very strong electrostatic forces between oppositely charged ions. Also called cation-anion forces.

Ionic bond (Sec 1.4A): A chemical bond formed between a cation and anion due to the electrostatic force of attraction between oppositely charged ions.

Ionic reaction (Sec 3.1A, 6.2, 6.6, 6.10, 8.3, 10.1): A reaction involving ions as reactants, intermediates, or products; the ions are usually produced through the heterolysis of covalent bonds.

Ionization (Sec 9.14): The conversion of molecules to ions

Ionization energy: Amount of energy required to remove an electron from some species.

IR spectroscopy (Sec 2.15, Lab 8.2): Type of optical spectroscopy that measures the absorption of infrared radiation (4000 - 400 cm^-1, or 2.5 - 25 μm), and it provides structural information about functional groups present in the compound being analyzed. Also called infrared spectroscopy.

IR-active vibration: A vibration of a bond that changes the dipole moment of a molecule, and thus can absorb IR light.

IR-inactive vibration: A vibration of a bond that does not change the dipole moment of a molecule, and thus cannot absorb IR light.

Isobutane: The common name for 2-methylpropane, (CH₃)₃CH.

Isobutyl group: The group formed by removing a hydrogen atom from one of the methyl groups of isobutane, or 2-methylpropane, (CH₃)₂CHCH₂ - . Also called the (2-methypropyl) group.

Isocyanate (Lab 25.11D): A compound with the formula R-N=C=O ; aryl isocyanates are used to prepare carbamate (urethane) derivatives of alcohols and phenols.

Isoelectric point (Sec 24.2C): The pH at which the number of positive and negative charges on an amino acid or protein are equal, and the overall charge is zero. Also called isoionic point.

Isolated diene (Sec 13.6): Diene whose C=C double bonds are separated by two or more single bonds; isolated double bonds react independently, as they do in a simple alkene.

Isomers (Sec 1.6, 5.2A): Different molecules that have the same molecular formula.

Isoprene unit (Sec 23.3): A name for a structural unit found in all terpenes.

Isotactic polymer: A polymer in which the configuration at each stereogenic center along the chain is the same.

Isotopes (Sec 1.2A): Different atomic forms of an element that have the same number of protons and are chemically identical, but contain different numbers of neutrons, and thus have different atomic mass numbers.

IUPAC System (Sec 4.3): A system for naming compounds through naming rules, with the fundamental principle that each different compound should have an unambiguous name; originally developed in 1892 by the International Union of Pure and Applied Chemistry

J

Jones oxidation (Sec 12.4C, Lab 25.7D, , Lab 25.11A): The use of chromic acid, H₂CrO₄ , and aqueous sulfuric acid in a solvent of acetone, to oxidize primary alcohols and aldehydes to carboxylic acids, and secondary alcohols to ketones, but it will not react with carbon-carbon double and triple bonds.

Jones reagent(Sec 12.4C, Lab 25.7D, Lab 25.11A): A very strong oxidizing agent that is prepared by mixing CrO₃ or Na₂CrO₄ with aqueous sulfuric acid in a solvent of acetone; it will oxidize primary alcohols and aldehydes to carboxylic acids, and it will oxidize secondary alcohols to ketones, but it will not react with carbon-carbon double or triple bonds.

K

Kekule structure (Sec 2.1D, 14.4): Structure in which lines are used to represent bonds, such as the structure of benzene, which is drawn as a hexagon of carbon atoms with alternating single and double bonds around the ring, and with one hydrogen atom attached to each carbon.

Ketal (Sec 16.7B): A derivative of a ketone having two alkoxy groups (-OR) in place of the carbonyl group, derived by adding two molar equivalents of an alcohol. Also called an acetal.

Keto-enol tautomerism (Sec 18.2): Rearrangement of an aldehyde or a ketone into its enol form: R₂CHCOR' ⇄ R₂C=C(OH)R'. Also called keto-enol tautomerization.

Ketone (Sec 2.9, 12.1, 16.1): A molecule containing an internal carbonyl group, >C=O , that is attached to two other carbon atoms, with the general formula RCOR' or RC(=O)R'.

Ketone hydrate (Sec 16.7): The geminal diol formed by addition of water across the carbonyl double bond of a ketone.

Kinetic control (Sec 7.6B, 13.9A, 18.4A): A principle stating that when the ratio of products of a reaction is determined by relative rates of reaction, as measured by their activation energies, and the most abundant product will be the one that is formed fastest. Also called rate control.

Kinetic energy (KE) (Sec 3.8): The energy of motion; energy that results from the motion of an object, defined as: KE = ½ m v² , where m is the mass of the object, and v is its velocity.

Kinetic enolate (Sec 18.4A, 19.5B): The enolate formed fastest from an unsymmetrical ketone, which usually has the least substituted double bond; it is favored by use of a very strong, sterically hindered base, such as LDA (lithium diisopropylamide), in an aprotic solvent that is unreactive with bases, such as an ether like THF (tetrahydrofuran) or DME (dimethoxyethane).

Kinetic-molecular theory: A theory of the behavior of matter at the molecular level, which states that all matter consists of submicroscopic particles that are in constant motion, and the higher the temperature, the faster the particles move.

Kinetic product (Sec 13.9): The product that is formed fastest; the major product under kinetic control.

Kinetic resolution (Sec 5.10B): Production of a preponderance of one stereoisomer over the other by a reaction in which the rates of the stereoisomers are different.

Kinetics (Sec 6.5): The study of the rate of a chemical reaction.

Knoevenagel condensation: Condensation of an aldehyde or ketone with an active hydrogen compound, which is catalyzed by a weak base, such as an amine.

Kolbe Reaction (Sec 21.8): Carboxylation of phenolate anions with carbon dioxide to form salicylic acids, or o-hydroxy benzoic acids. Also called the Kolbe-Schmitt Reaction.

L

Lactam (Sec 17.8 I): A cyclic amide; δ-aminoacid can undergo an intramolecular condensation to produce δ-lactams, which contain a six-membered ring.

Lactone (Sec 17.7C): A cyclic ester; δ-hydroxyacids can undergo an intramolecular esterification to produce δ-lactones, which contain a six-membered ring.

LCAO Method (Linear Combination of Atomic Orbitals Method) (Sec 1.11): Wave functions, ψ, for molecular orbitals are obtained by combinining, in a linear fashion (addition or subtraction), the wave functions for the atomic orbitals.

Le Chatelier's principle (Lab 10.3, 20.2): If a system in chemical equilibrium is disturbed, then the equilibrium shifts to counteract the disturbance, and a new equilibrium is established. For example, adding more of a reactant, or removing a product, will shift the equilibrium to the right and increase the yield of products. Also spelled Le Châtelier.

Leaving group (Sec 6.2, 6.4, 6.13E, 17.4, Lab 14): The substituent that departs with a lone pair of electrons from the substrate in a nucleophilic substitution reaction; good leaving groups depart as stable, very weak bases.

Lenz's Law: The current induced in a circuit will flow in a direction that produces a magnetic field opposing the change in flux that produces the current.

Leveling effect of a solvent (Sec 3.14): An effect that restricts the use of certain solvents with strong acids and bases; no acid stronger than the conjugate acid of the solvent, and no base stronger than the conjugate base of the solvent, can exist to an appreciable extent in that solvent.

Levorotation (Sec 5.8B): (1) A turning or twisting to the left. (2) The counterclockwise turn given the plane of plane-polarized light by solutions of levorotatory optically active compounds.

Levorotatory (Sec 5.8B): An optically active compound that rotates plane-polarized light counterclockwise; designated l or (-).

Lewis acid (Sec 3.3, 15.3, 15.6, 15.7): A compound that is an acid because it is an electron pair acceptor; common examples include AlCl₃ , ZnCl₂ , FeCl₃ , FeBr₃ , and BF₃ .

Lewis base (Sec 3.3): A base that is an electron pair donor.

Lewis structure (Sec 1.3 - 1.5): A representation of a molecule showing each electron pair as two dots ( : ) or a dash ( - ). Also called electron-dot structure.

Lewis theory of acids and bases (Sec 3.2B): An acid is an electron pair acceptor, and a base is an electron pair donor.

LCAO Method (Linear Combination of Atomic Orbitals Method) (Sec 1.11): Wave functions, ψ, for molecular orbitals are obtained by linearly combining (addition or subtraction) the wave functions for the atomic orbitals.

Lipid (Sec 23.1): A substance of biological origin that is soluble in nonpolar solvents. Lipids include fatty acids, triacylglycerols (fats and oils), steroids, prostaglandins, terpenes, terpenoids, and waxes.

Lipophilic group (Sec 2.13D, 11.2, 16.3, 17.2, 23.2, Lab 5.3): A nonpolar (lipid loving) group that avoids an aqueous surrounding and seeks a nonpolar environment. Also called hydrophobic.

Liquid-liquid extraction (Lab 5.3): The process of removing a compound from a mixture by distributing a solute between two immiscible liquids, the extracting phase, Sx, and the original phase, So.

Lithium aluminum hydride, LiAlH₄ (Sec 12.3): A powerful reducing agent that is usually used in an anhydrous ether solution, and followed by an aqueous acid work-up; it reduces carboxylic acids, carboxylic esters, aldehydes and ketones into alcohols, and it reduces amide, nitro, nitrile, imine, oxime and azide compounds into amines, but it will not react with carbon-carbon double and triple bonds.

Lithium diisopropylamide (Sec 18.4, 19.5B): A very strong, sterically hindered base, ( i-C₃H₇ )₂ N‾ Li⁺ , whose conjugate acid has pK_a = 38. Abbreviated LDA.

London dispersion forces (Sec 2.13B, 4.12B): Weak attractive forces between induced dipoles that exist between all molecules, that are produced when a temporary unsymmetrical electron distribution produces a temporary polarity in an atom, which induces a temporary polarity of opposite charge in an adjacent atom. The strength of London dispersion force increases with increasing polarizability of the atoms and increasing surface area of the molecule. Also called London forces, or dispersion forces.

Lone pair: A pair of valence electrons that belongs solely to one atom, and does not contribute to bonding in a covalent molecule. Also called unshared electron pair, or nonbonding electron pair.

Lucas test (Lab 25.11B): A test used to determine whether an alcohol is primary, secondary, or tertiary. The test measures the rate of reaction with the Lucas reagent, ZnCl₂ in concentrated HC1. Tertiary alcohols react fast, secondary alcohols react more slowly, and primary alcohols react very slowly.

LUMO (Sec 3.3A, 13.8C): The lowest unoccupied molecular orbital; when a molecule in the ground state is excited, an electron may jump from a HOMO into a LUMO.

M

Macromolecule (Sec 10.11): A very large molecule.

Magnetic resonance imaging (Sec 9.12): A technique based on NMR spectroscopy that is used in medicine. Also called MRI.

Magnetic shielding (Sec 9.5, Lab 8.3): In ¹H NMR, the circulation of sigma and pi electrons within a chemical bond produces an internal electric field that induces an internal magnetic field, B_i , about the nuclei, which acts to oppose the applied magnetic field, B₀ , and causes the effective magnetic field, B_e , at the nuclei to be smaller, according to the formula: B_e = B₀ - B_i . Protons in electron dense environments are partially shielded and sense a smaller effective magnetic field, B_e , so they absorb upfield (to the right) at smaller delta values, and at lower radio frequencies (or higher external magnetic fields).

MALDI (Sec 9.18A): A technique in which an analyte is mixed with low molecular weight organic molecules that are known for their ability to absorb and transfer energy from the laser to the analyte in the mass spectrometer. Also called Matrix-assisted laser desorption ionization.

Malonic ester synthesis (Sec 18.7): Synthesis based on the strongly activated methylene group of malonic esters, which easily deprotonate in base to form a resonance-stabilized anion that can be alkylated or acylated to produce a monoalkyl or dialkyl malonic ester; subsequent hydrolysis of the ester and decarboxylation produces a monosubstituted or disubstituted acetic acid.

Mannich reaction (Sec 19.8): The reaction of the enol form of a carbonyl compound with the imine derived from formaldehyde and a primary or secondary amine to produce a β-aminoalkyl carbonyl compound (Mannich base).

Map of electrostatic potential (Sec 1.8, 2.2A): Computer generated structure that uses color to show the relative distribution of electron density at the Van der Waals surface of a molecule or ion; violet shows electron-poor regions that have a positive charge (+); blue to blue-green show regions that have a partial positive charge (δ+); green shows regions of normal electron density with no charge (0); yellow to orange show regions that have a partial negative charge (δ─); red shows electron-rich regions that have a negative charge (─). Also called electrostatic potential map.

Markovnikov addition (Sec 8.2 - 8.6, 8.19, 10.9A): An electrophilic addition reaction between hydrogen halide, HX, and an unsymmetrical alkene, where the hydrogen adds to the less substituted carbon, and the halogen adds to the more substituted carbon, which produces the more substituted alkyl halide.

Markovnikov's rule (Sec 8.2 - 8.6): When a hydrogen halide, HX, reacts with the C=C group of an unsymmetrical alkene, the hydrogen atom adds to the carbon with the most hydrogen atoms (the less substituted carbon), and the halide ion adds to the carbon with the fewer hydrogen atoms (the more substituted carbon). This rule can predict the regiochemistry for ionic addition of a polar reagent to a double bond: the positive portion of the adding reagent attaches itself to a carbon atom of the double bond so as to yield the more stable carbocation as an intermediate.

Mass number (Sec 1.2): Sum of the number of protons and neutron in the nucleus of an atom, which determines over 99.9% of the mass of that atom. Also called atomic mass number.

Mass spectrometry (Sec 9.13 - 9.19): A technique, useful in structure elucidation, that is based on generating ions of a molecule in a magnetic field, then instrumentally determining the mass to charge ratio, and relative amounts of the ions that result. Also called MS.

Matrix-assisted laser desorption ionization (Sec 9.19): A technique in which an analyte is mixed with low molecular weight organic molecules that are known for their ability to absorb and transfer energy from the laser to the analyte in the mass spectrometer. Also called MALDI.

Mean: A measure of central tendency; the arithmetic average of a set of values, calculated as the sum of the values divided by the number of values.

Mechanism of reaction (Sec 3.13, 6.6, 6.10): A step-by-step description of the events that take place at the molecular level as reactants are converted to products, including a description of all intermediates and transition states. Also called reaction mechanism.

Meisenheimer intermediate (Sec 21.11A): A cyclohexadienyl anion that is resonance stabilized by delocalization of electrons, which is an intermediate that is formed during a nucleophilic aromatic substitution (S_NAr) reaction by an addition-elimination mechanism.

Melting point (Sec 2.13A, Lab 3.3): The temperature at which an equilibrium exists between the well ordered crystalline state and the more random liquid state, and which the solid has the same vapor pressure as the liquid in equilibrium with it.

Melting point range (Lab 3.3): The experimentally determined range of temperatures at which a solid melts. The first point (lower temperature) is the temperature at which the first drop of liquid forms in a crystalline solid, and the second point (higher temperature) is the temperature at which the entire mass of solid turns to a clear liquid.

Mercaptan: A molecule containing a sulfhydryl (mercapto) group, -SH, which is the sulfur analogue of an alcohol. Also called a thiol.

Meso compound (Sec 5.12B): An optically inactive compound that is achiral, even though it contains chirality centers (tetrahedral atoms with four different groups attached), which is usually a result of having a plane of symmetry in the molecule.

Mesylate (Sec 11.10): A methanesulfonate ester (ester of an alcohol with methanesulfonic acid); the mesylate group is an excellent leaving group.

Meta (Sec 14.2): Having a 1,3 relationship on a benzene ring.

Meta director (Sec (15.10, 15.11): A group that when present on a benzene ring, directs an incoming electrophile to a position meta to itself.

Methanide migration (Sec 7.8A): Migration of a methanide ion, H₃C:^- , from a carbon adjacent to a carbocation, which usually forms a more stable carbocation. Also called methanide rearrangement.

Methine group: The >CH- group; obtained by removing three hydrogen atoms from methane.

Methyl group (Sec 2.4A): The CH₃- group; obtained by removing one hydrogen atom from methane, CH₄ .

Methylene (Sec 8.14A): The carbene with the formula :CH₂ ; it is a highly unstable compound that has an uncharged divalent carbon atom with a lone pair of electrons.

Methylene group (Sec 2.4B): The -CH₂- group; obtained by removing two hydrogen atoms from methane, CH₄ .

Micelle (Sec 23.2C): A spherical cluster of ions in aqueous solution (such as those in soapy water) in which the nonpolar groups are in the interior, and the ionic (or polar) groups are at the surface.

Michael addition (Sec 18.9, 19.7, Lab 18.4): Base-promoted conjugate addition (1,4-addition) of a resonance stabilized carbanion nucleophile, such as a deprotonated active hydrogen compound (Michael donor), to an electrophilic conjugated double bond, such as an α,β-unsaturated carbonyl compound (Michael acceptor). Also called Michael reaction or Michael condensation.

Mixed melting point (Lab 3.3): The melting point range will be broad when a pure solid compound contains impurities.

Mixed solvents (Lab 3.2): Use of two solvents for recrystallization, where the pure solid compound is very soluble in the first hot solvent, but less soluble in the other solvent.

Molar absorptivity (ε) (Sec 13.8B, Lab 8.4): The molar absorptivity, ε, is determined by UV-Vis spectroscopy, and defined by the Beer-Lambert Law: ε = A / c l , where A is the absorbance at a particular wavelength (λ), c is the concentration in mol/L, and l is the path length in cm of the light beam through the sample cell. Also called the molar extinction coefficient.

Molecular formula (Sec 1.6): A chemical formula that gives the total number of atoms of each element present in one molecule of a compound

Molecular geometry (Sec 1.16): The shape of a region of a molecule or ion, which is determined by the arrangement in three-dimensional space of a central atom and the atoms directly attached to it; nonbonding electron pairs occupy spacial positions around that central atom, but only the locations of bonding electron pairs define the name of the shape at that central atom.

Molecular ion (Sec 9.14 - 9.17): (1) The radical cation that has a +1 charge and an unshared electron, M∙⁺, which is produced in a mass spectrometer when one electron is dislodged from the parent molecule. (2) An ion that contains two or more atoms covalently bonded, which can be formed by deprotonation of an acidic molecule, protonation of a basic molecule, or formation of an organic reaction intermediate. Also called a polyatomic ion.

Molecular orbital (Sec 1.11, 1.15): Orbital that encompasses two or more atoms in a molecule. When atomic orbitals combine to form molecular orbitals, the number of molecular orbitals that result will always equal the number of atomic orbitals that combine. Abbreviated MO.

Molecular sieves (Lab 2.24): Dehydrated zeolite crystals with well-defined pore sizes to admit molecules smaller than the pores; often used as a drying agent to adsorb water from solvents or reactions.

Molecularity (Sec 6.5B): The number of species involved in a single step of a reaction (usually the rate determining step).

Molecule (Sec 1.3B): The smallest uncharged individual unit of a compound that retains the composition and properties of that compound.

Mole Fraction (Lab 4.4): The moles of compound X divided by the total moles in solution:

N_X = n_X / ( n_X + n_Y + n_Z + ... )

Monomer (Sec 10.11): The subunit (simple starting compound) from which a polymer is made.

Monosaccharide (Sec 22.1A): The simplest type of carbohydrate, one that does not undergo hydrolytic cleavage to a simpler carbohydrate.

Mother liquor (Lab 3.2): Filtrate from recrystallization

MRI (Sec 9.12): A technique based on NMR spectroscopy that is used in medicine. Also called magnetic resonance imaging.

Multiplet (Sec 9.2C, 9.9, Lab 8.3): A group of peaks resulting from signal splitting; a singlet is a signal with only one peak; a doublet is a signal with two peaks; a triplet is a signal with three peaks; a quartet is a signal with four peaks; a quintet is a signal with five peaks; a sextet is a signal with six peaks; a septet is a signal with seven peaks; etc.

Mutarotation (Sec 22.3): The spontaneous change that takes place in the optical rotation of α and β anomers of a sugar when they are dissolved in water. The optical rotations of the sugars change until they reach the same value.

m/z Ratio (Sec 9.13): The mass to charge ratio of the ions detected by mass spectrometry, where m is mass and z is charge.

N

n + 1 Rule (Sec 9.2C, Lab 8.3): The ¹H NMR signal may be split into a multiplet with (n + 1) peaks, when it has n number of nonequivalent hydrogen neighbors that are separated by 2 or 3 covalent bonds.

Nanotube (Sec 14.8C): A form of elemental carbon composed of a cylindrical cluster of carbon atoms.

Neat liquid (Lab 8.2): A pure liquid.

Neighboring group participation (Problem 6.42): The effect on the course or rate of a reaction brought about by another group near the functional group undergoing reaction.

Neopentane (Sec 4.3): An isomer of pentane: 2,2-dimethylpropane.

Neopentyl group (Sec 4.3): The 2,2-dimethylpropyl group.

Newman projection formula (Sec 4.8): A means of representing the spatial relationships of groups attached to two atoms of a molecule; when viewing the molecule from one end directly along the bond axis joining the two atoms, bonds that are attached to the front atom are shown as radiating from the center of a circle; and those attached to the rear atom are shown as radiating from the edge of the circle.

Ninhydrin (Sec 24.4A): A reagent that reacts with most amino acids to give a derivative with an intense purple color, with λ_max = 570 nm.

Nitration (Sec 15.4): Replacement of a hydrogen atom by a nitro group, -NO₂.

Nitrile (Sec 2.11, 17.2I, 17.8G): A molecule containing a cyano group, -C≡N , with the general formula RCN.

Nitrogen rule (Sec 9.17A): A rule that states that if the mass of the molecular ion in a mass spectrum is an even number, the parent compound contains an even number of nitrogen atoms (zero is an even number).

Nitronium ion (Sec 15.4, Lab 15.4): The NO₂⁺ ion, O=N⁺=O, which is a strong electrophile that is often used in aromatic nitration.

Nitrosoamine (N-nitrosoamine) (Sec 20.6C): An amine with a nitroso group, -N=O, bonded to the amine nitrogen atom; the reaction of secondary amines with nitrous acid gives secondary nitrosoamines.

Node (Sec 1.15): A place where a wave function (ψ) is equal to zero. The greater the number of nodes in an orbital, the greater is the energy of the orbital.

Nomenclature (Sec 4.3): A system for naming compounds. See functional class nomenclature and substitutive nomenclature.

Nonaromatic compound (Sec 14.7D): A cyclic conjugated system whose pi electron energy is the same as that of the corresponding open-chain compound.

Nonbenzenoid aromatic compound (Sec 14.8B): An aromatic compound that does not contain any benzene rings; examples include azulene, the aromatic ions, and the aromatic annulenes that contain more than six carbon atoms.

Normal boiling point (Lab 4.2): The boiling point of a liquid that is measured at 760 torr (1 atm).

Normal phase chromatography (Lab 6.3): A form of chromatography in which a polar stationary phase (adsorbent) is used with a less polar mobile phase (eluting solvent), and polar compounds bind much more tightly than nonpolar compounds; common adsorbents are alumina and silica gel.

Nuclear Magnetic Resonance Spectroscopy (Sec 9.2 - 9.12, Lab 8.3): A spectroscopic method for measuring the absorption of radio frequency radiation by certain nuclei when the nuclei are in a strong magnetic field. The most common are ¹H NMR spectra and ¹³C NMR spectra, which provide structural information about the carbon framework of a molecule, and the number and environment of hydrogen atoms attached to each carbon atom. Also called NMR spectroscopy.

Nucleic acids (Sec 25.1): Biological polymers of nucleotides. DNA preserves, and RNA transcribes the hereditary information within cells.

Nucleophile (Sec 3.4A, 6.3, 6.13B, 8.1, Lab 14): A "nucleus loving" species; an anion or molecule with a lone pair of electrons that donates its electron pair to form a new covalent bond; Lewis bases (electron-pair donors) are nucleophiles.

Nucleophilic acyl substitution (Sec 17.4, 21.11A, Lab 20.1): Two-stage substitution reaction, in which one type of carboxylic acid derivative is converted into another, which involves addition and elimination reactions; in the addition stage, the nucleophile adds to the carbon that bears the leaving group; in the elimination stage, the leaving group is expelled. Also called acyl transfer reaction, or nucleophilic addition-elimination reaction.

Nucleophilic addition (Sec 12.1A, 16.6, 17.4, 19.1): A reaction in which a nucleophile adds to a substrate containing a polar multiple bond between carbon and a heteroatom (such as a carbonyl group, >C=O , or a nitrile group, -C≡N ); when a nucleophile attacks the δ+ carbon of a carbonyl group, an alkoxide anion intermediate is initially formed, which subsequently attacks an electrophile, such as H⁺ .

Nucleophilic addition-elimination mechanism (Sec 17.4, 21.11A): Two-stage mechanism for a nucleophilic addition-elimination reaction; in the addition stage, the nucleophile adds to the carbon that bears the leaving group, then in the elimination stage, the leaving group is expelled.

Nucleophilic aromatic substitution (Sec 21.11A): Two-stage substitution that involves addition and elimination reactions of an aromatic compound; in the addition stage, a nucleophile adds to the aromatic ring; in the elimination stage, a group is expelled from the aromatic ring. Also called S_NAr reaction.

Nucleophilic substitution reaction (Sec 6.2, 6.5 - 6.14, Lab 14): A reaction initiated by a nucleophile that reacts with a substrate and replaces a leaving group that departs with a lone pair of electrons.

Nucleophilicity (Sec 6.13B): The strength of a nucleophile, as measured by its rate of reaction in S_N2 or E2 reactions (a kinetic property); the stronger the nucleophile, the faster its rate of reaction.

Nucleoside (Sec 22.15A, 25.2): A five-carbon monosaccharide bonded at the l' position to a purine or pyrimidine.

Nucleotide (Sec 25.2): A five-carbon monosaccharide bonded at the l' position to a purine or pyrimidine, and at the 3' or 5' position to a phosphate group.

O

Occlusion (Lab 3.2): The inclusion of one substance within another (as in a gelatinous precipitate).

Octet rule (Sec 1.3, 1.4): Main group elements heavier than boron tend to gain, lose, or share electrons so as to have eight valence electrons, which will achieve the electron configuration of the nearest noble gas.

Olefin (Sec 7.1): An old name for an alkene.

Optical purity (Sec 5.9B): A measure of the enantiomeric excess; calculated for a mixture of enantiomers by dividing the observed specific rotation for the mixture by the specific rotation of the pure enantiomer, then multiplying by 100%.

Optically active compound (Sec 5.8, 5.9): A compound that rotates the plane of polarization of plane-polarized light.

Orbital (Sec 1.10): A region of space around a substance in which there is a high probability of finding an electron, which can be described mathematically by squaring the wave function. Each orbital has a characteristic energy and can hold two electrons when their spins are paired.

Ordinate: The vertical axis in a set of two-dimensional coordinates; commonly referred to as the Y-axis.

Organolithium compound (Sec 12.6, 12.7): A compound that contains a carbon-lithium bond, RLi, which is a common source of carbanions; it is formed by the reaction of lithium with an alkyl halide or aryl halide.

Organometallic compound (Sec 12.5): A compound that contains a carbon-metal bond.

Ortho (Sec 14.2): Having a 1,2 relationship on a benzene ring.

Ortho-para director (Sec 15.10, 15.11): A group that, when present on a benzene ring, directs an incoming electrophile to a position ortho and/or para to itself.

Overall relative stabilities of alkenes (Sec 7.3B): The greater the number of attached alkyl groups, (i.e. the more highly substituted the carbon atom of the double bond) the greater the alkene's stability.

Overtone in IR: A weak absorption in the IR spectrum that occurs at approximately twice the fundamental vibration frequency of a very strong absorption, due to harmonic oscillations.

Oxidation (Sec 12.2, 12.4): A reaction that results in a loss of electrons, or that increases the oxidation state of an atom in a molecule or ion. Oxidation of an organic compound usually involves increasing its oxygen content, decreasing its hydrogen content, or adding a strongly electronegative atom.

Oxidative cleavage of alkenes (Sec 8.17A): A reaction that cleaves an alkene at its double bond with a strong oxidizing agent, such as potassium permanganate, KMnO₄ , which converts the resulting fragments into ketones, carboxylic acids, and/or carbon dioxide.

Oxide ion (Sec 3.15, 11.6, 16.6): A chemical species with an oxygen atom that bears a formal negative charge, such as a deprotonated alcohol, RO^- , or a reaction intermediate formed after a nucleophile attacks a δ+ carbonyl carbon, R₂ C(Nu)O^- . Also called an oxide anion.

Oxidizing agent (Sec 12.2): A substance that causes an increase in the oxidation state of another substance; the oxidizing agent is reduced during the course of the reaction.

Oxime (Sec 16.8B): A compound containing the -C=N-OH group, formed by the reaction of an aldehyde or ketone with hydroxylamine, NH₂OH.

Oxirane (Sec 11.13, 11.14): A cyclic ether with a three-membered ring, containing one oxygen and two carbon atoms. Also called an epoxide.

Oxonium ion (Sec 3.12, 11.12, 16.6): A chemical species with an oxygen atom that bears a formal positive charge, such as a protonated alcohol, RO⁺H₂ , a protonated ether, RO⁺(H)R', or a protonated carbonyl compound, R₂ C=O⁺H. Also called an oxonium cation.

Oxymercuration (Sec 8.5, 11.4): The addition of -OH and -HgO₂CR to a multiple bond.

Oxymercuration-demercuration of alkenes (Sec 8.6, 11.4): A two-step method that converts an alkene into an alcohol, with Markovnikov regiochemistry, and usually no rearrangements. The first step is oxymercurationthat reacts the alkene with water and mercuric acetate, Hg(OOCCH₃ )₂ , which adds a hydroxyl group, -OH, and an acetoxymercury group, -HgOOCCH₃ , to adjacent carbons of the double bond. The second step is demercuration that reduces the first product with sodium borohydride, NaBH₄ , which removes the acetoxymercury group and replaces it with hydrogen, to produce the more substituted alcohol as a mixture of syn and anti addition products.

Ozonolysis (Sec 8.17B): A reaction that cleaves an alkene at its double bond with ozone, O₃ , which forms a cyclic ozonide, followed by reduction with either dimethyl sulfide, (CH₃)₂S, or zinc/acetic acid, which converts the resulting fragments into ketones and/or aldehydes.

P

p Orbitals (Sec 1.10): A set of three degenerate (equal energy) atomic orbitals; the principal quantum number n ≥ 2; the azimuthal quantum number l = 1; the magnetic quantum numbers m are +1, 0, -1.

Para (Sec 14.2): Having a 1,4 relationship on a benzene ring.

Paraffin (Sec 4.15): An old name for an alkane.

Partition coefficient (Lab 5.3): A quantitative expression, K, for the amount of a substance, A, that dissolves in two separate immiscible solvents, where K is equal to the solubility of A in g/ml in the extracting solvent, Sx, divided by the solubility of A in the original solvent, So. Also called the distribution coefficient.

Pauli exclusion principle (Sec 1.10A): No two electrons of an atom may have the same set of four quantum numbers; thus only two electrons can occupy the same orbital, and then only when their spin quantum numbers are opposite (spins are paired).

PCC (Pyridinium chlorochromate) (Sec 12.4D): A complex of chromium trioxide with pyridine and HCl; PCC oxidizes primary alcohols to aldehydes.

Periplanar (Sec 7.6D): A conformation in which two adjacent atoms, and two of the vicinal groups that are bound to them, all lie in the same plane. Also called coplanar.

Peroxide (Sec 10.lA): Compound with the general formula ROOR, that contains an oxygen-oxygen single bond.

Peroxy acid (Sec 11.13A): An acid with the general formula RCO₃H, that contains a carbon-oxygen double bond and an oxygen-oxygen single bond. Also called a peracid.

Petroleum ether (Lab 3.2): A mixture of volatile aliphatic hydrocarbons obtained from refining petroleum; does not contain the ether functional group.

Phase (Sec 2.14): Whether a substance is a solid, liquid, gas, or plasma. Also called physical state.

Phase sign (Sec 1.9): Signs, either + or -, that are characteristic of all equations that describe the amplitudes of waves.

Phase-transfer catalyst (Sec 11.16): A reagent that transports an ion from an aqueous phase into a nonpolar phase where reactions take place more rapidly; common phase-transfer catalysts are crown ethers and quaternary ammonium halides, R₄N⁺X^-.

Phenol (Sec 14.2, 21.1): (1) Hydroxybenzene, C₆H₅OH. (2) Family of compounds characterized by a hydroxyl group on an aromatic ring, ArOH.

Phenols as weak acids (Sec 21.5A): Simple phenols, ArOH, are weak acids with pK_a ≈ 10 and they are deprotonated by aqueous NaOH to form phenoxide anions, ArO^-.

Phenyl group (Sec 2.4B, 6.1, 14.2): The C₆H₅- group; obtained by removing a hydrogen atom from benzene, C₆H₆ . Abbreviated Ph- or φ- .

Phosphatidic acids (Sec 23.6): Derivatives of glycerol in which two hydroxyl groups are joined to fatty acids, and one terminal hydroxyl group is joined in an ester linkage to phosphoric acid.

Phospholipid (Sec 23.6): Compounds that are structurally derived from phosphatidic acids. In a phospholipid, the phosphate group of the phosphatidic acid is joined in ester linkage to a nitrogen-containing compound such as choline, 2-aminoethanol, or L-serine.

Photon (Sec 2.15, 9.2, 13.9, Lab 8): A massless packet of electromagnetic energy, with energy equal to Planck's constant (6.6260693 × 10^-34 J s) times the frequency: E = h ∙ υ.

Physical properties (Sec 2.13): Properties of a substance that can be measured without changing its chemical composition, such as melting point, boiling point, density, refractive index, and solubility in common solvents.

Physical state (Sec 2.14): Whether a substance is a solid, liquid, gas, or plasma. Also called phase.

Pi (π) bond (Sec 1.13): A bond formed when electrons occupy a bonding pi molecular orbital (i.e., the lower energy molecular orbital that results from overlap of parallel p orbitals on adjacent atoms).

Pi (π) molecular orbital (Sec 1.13): A molecular orbital formed when parallel p orbitals on adjacent atoms overlap. Pi molecular orbitals may be bonding (p lobes of the same phase sign overlap) or antibonding (p orbitals of opposite phase sign overlap).

pK_a (Sec 3.5): The negative logarithm of the acidity constant, K_a ; pK_a = ─log K_a

Plane of symmetry (Sec 5.6, 5.12A): An imaginary plane that bisects an achiral molecule in a way such that the two halves of the molecule are mirror images of each other.

Plane-polarized light (Sec 5.8A): Ordinary light in which the oscillations of the electrical field occur only in one plane.

Polar aprotic solvent (Sec 6.13C): A solvent that has a strong dipole moment, but does not have acidic protons; it is an excellent solvent for S_N2 reactions because it does not decrease nucleophilicity; it will not solvate anions (such as negatively charged nucleophiles), but it will solvate cations (such as metal cations); common polar aprotic solvents include acetone, DMF, DMSO and DMA.

Polar covalent bond (Sec 2.2): A covalent bond in which the electrons are not shared equally because of differing electronegativities of the bonded atoms.

Polar molecule (Sec 2.3): A molecule that has a dipole moment.

Polarimeter (Sec 5.8B): A device used for measuring optical activity.

Polarizability (Sec 2.13B, 6.13C): The susceptibility of the electron cloud of an uncharged atom to distortion by the influence of an electric charge; larger atoms have greater polarizability than smaller atoms.

Polyamide: A polymer in which the monomer units are bonded by amide linkages, such as nylon.

Polycarbonate: A polymer in which the monomer units are bonded together by carbonate ester linkages.

Polycyclic compound (Sec 4.14): A molecule with two or more fused rings.

Polyester: A polymer in which the monomer units are bonded by ester linkages.

Polyether (Sec 11.14A): A water soluble polymer of repeating ether groups, RO-(RO-)_n-ROH; an example is poly(ethylene glycol), or carbowax, which is produced by the anionic polymerization of ethylene oxide with methoxide anion.

Polymer (Sec 10.11): A large molecule made up of many repeating subunits. For example, the polymer polyethylene is made up of repeating ethylene subunits, -(CH₂ CH₂)_n -

Polymerization (Sec 10.11): Reaction that joins monomer molecules together to form a polymer.

Polysaccharide (Sec 22.1A): A carbohydrate that, on a molecular basis, undergoes hydrolytic cleavage to yield many molecules of a monosaccharide.

Polyurethane: A polymer in which the monomer units are bonded together by carbamateester (urethane) linkages.

Potential energy (PE) (Sec 3.8): Stored energy; the energy that results from an object’s position in a field of force, or energy due to attractive or repulsive forces between objects. .

Potential energy diagram (Sec 4.8): A graph of the energy difference between conformations of a molecule.

Pot temperature (Lab 4.3): The temperature of the boiling liquid in the stillpot in a distillation apparatus.

Primary carbon (Sec 2.5): Carbon atom that has only one other carbon atom attached to it

Primary protein structure (Sec 24.1, 24.5): The covalent structure of a polypeptide or protein, which is determined by the sequence of amino acids in the protein.

Prochiral (Sec 12.3D): A group is prochiral if replacement of one of two identical groups at a tetrahedral atom, or if addition of a group to a trigonal planar atom, leads to a new stereogenic center. At a tetrahedral atom where there are two identical groups, the identical groups can be designated pro-R and pro-S depending on what configuration would result when it is imagined that each is replaced by a group of next higher priority (but not higher than another existing group).

Protecting group (Sec 11.11, 12.9, 15.15, 16.7C): A group that is introduced into a molecule to protect a sensitive group, while the reaction is carried out at some other location in the molecule; the protecting group is later removed in a subsequent reaction.

Protein (Sec 24.1, 24.4): A large biological polymer of α-amino acids joined by amide linkages.

Protic solvent (Sec 3.12, 6.13C): A solvent that has acidic protons, usually due to hydrogen bound to oxygen atoms, which can form hydrogen bonds to many solute molecules; it solvates both cations and anions; it is an excellent solvent for S_N1 reactions because it stabilizes the S_N1 transition state and the carbocation intermediate; common protic solvents include water, alcohols, and carboxylic acids.

Proton decoupling (Sec 9.11B): An electronic technique used in ¹³C NMR spectroscopy that allows decoupling of spin-spin interactions between ¹³C nuclei and ¹H nuclei. In spectra obtained in this mode of operation all carbon resonances appear as singlets.

Proton off-resonance decoupling (Sec 9.11D): An electronic technique used in ¹³C NMR spectroscopy that allows one-bond couplings between ¹³C nuclei and ¹H nuclei. In spectra obtained in this mode of operation, CH₃ groups appear as quartets, CH₂ groups appear as triplets, CH groups appear as doublets, and carbon atoms with no attached hydrogen atoms appear as singlets.

Psi function (ψ function or wave function) (Sec 1.9): A mathematical expression derived from quantum mechanics corresponding to an energy state for an electron. The square of the ψ function, ψ², gives the probability of finding the electron in a particular location in space.

Pyranose (Sec 22.2C): A sugar in which the cyclic acetal or hemiacetal ring is six membered.

Pyridinium chlorochromate, PCC (Sec 12.4A): A complex formed when chromium trioxide, CrO₃ , is dissolved in hydrochloric acid and then treated with pyridine, C₅H₅N. In a solvent of dichloromethane, CH₂Cl₂ , PCC will oxidize primary alcohols to aldehydes, and it will oxidize secondary alcohols to ketones, but it will not react with carbon-carbon double and triple bonds.

Q

Quantum mechanics (Sec 1.9): A theory of atomic and molecular structure that explains bonding in molecules, where the total energy of the system can be described by a mathematical expression called a wave equation, which is used to calculate the energy associated with the state of the electron and the relative probability of an electron residing in a given region of space.

Quaternary ammonium salt (Sec 20.2, 20.3): An amine where the nitrogen has 4 covalent bonds and a positive charge; usually containing a counter ion, such as chloride.

Quaternary carbon (Sec 2.5): Carbon atom that has four other carbon atoms attached to it.

Quaternary protein structure (Sec 24.1, 24.8): Only present in proteins containing 2 or more polypeptide chains.

Quinone (Sec 21.10): A derivative of cyclohexadienedione, usually 1,4-benzoquinone (para-quinone); oxidation of a 1,4-benzenediol (hydroquinone) derivative will produce a para-benzoquinone derivative.

R

R (Sec 2.4A): A symbol used to designate an alkyl group. It is often taken to symbolize any organic group.

R,S System (Sec 5.7): A method for designating the configuration of chirality centers.

Racemic mixture (Sec 5.9 - 5.10): An equimolar mixture of enantiomers that is optically inactive; designated (+). Also called racemate, or racemic form.

Racemization (Sec 5.10, 6.12A): A reaction that transforms an optically active compound into a racemic form, which occurs when a reaction causes chiral molecules to be converted into an achiral intermediate.

Radical (Sec 3.1A, 10.1, 10.6, 10.7): An uncharged electron deficient chemical species with an odd number of valence electrons due to an orbital with an unpaired electron; examples include the chlorine radical atom, Cl∙ , the tert-butyl radical, (CH₃)₃ C∙ , etc. Also called a free radical.

Radical addition of HBr to alkenes (Sec 8.2D, 10.10): An anti-Markovnikov addition reaction between hydrogen bromide, HBr, and an unsymmetrical alkene in the presence of peroxides, which produces the less substituted alkyl bromide; the mechanism involves addition of a bromine radical to the less substituted carbon, which produces the more substituted carbon radical that subsequently adds hydrogen.

Radical polymerization (Sec 10.10): An alkene polymerization reaction that proceeds via radical intermediates. Also called free-radical polymerization.

Radical reaction (Sec 10.1B): A reaction involving homolysis of covalent bonds that produces radicals.

Raney nickel (Sec 16.7D): A finely divided, hydrogen-bearing form of nickel made by treating a nickel-aluminum alloy with strong sodium hydroxide; the aluminum in the alloy reacts to form hydrogen, leaving a finely divided nickel powder saturated with hydrogen. Raney nickel desulfurization of thioacetals will leave a reduced methylene group.

Raoult's Law (Lab 4.3): The quantitative relationship between vapor pressure and composition of homogeneous liquid mixtures; the partial pressure of compound X, P_X , over a solution equals the vapor pressure, P_X⁰ , of pure X at a given temperature times the mole fraction of X, N_X , in the mixture: P_X = P_X⁰ N_X

Rate control (Sec 13.10A): A principle stating that when the ratio of products of a reaction is determined by relative rates of reaction, the most abundant product will be the one that is formed fastest. Also called kinetic control.

Rate-determining step (Sec 6.9): The slowest step in a multistep reaction, which determines the rate of the overall reaction. Abbreviated rds.

Reaction coordinate (Sec 6.7): The x-axis in an energy diagram that represents the progress along a reaction pathway that must take place as reactants are converted into products.

Reaction mechanism (Sec 3.13, 6.6, 6.10): A step-by-step description of the events that take place at the molecular level as reactants are converted to products, including a description of all intermediates and transition states.

Rearrangement reaction (Sec 3.1, 7.8, 11.4): A reaction in which the carbon skeleton of a molecule is rearranged to produce a different isomer of the original molecule.

Reducing agent (Sec 12.2, 12.3): A substance that causes a decrease in the oxidation state of another substance; the reducing agent is oxidized during the course of a reaction.

Reducing sugar (Sec 22.6A): Sugars that reduce Tollens' or Benedict's reagents. All sugars that contain hemiacetal or hemiketal groups (and therefore are in equilibrium with aldehydes or a-hydroxyketones) are reducing sugars. Sugars in which only acetal or ketal groups are present are nonreducing sugars.

Reduction (Sec 12.2, 12.3): A reaction that results in a gain of electrons, or that decreases the oxidation state of an atom in a molecule or ion. Reduction of an organic compound usually involves increasing its hydrogen content, decreasing its oxygen content, or removing a strongly electronegative atom.

Reductive amination (Sec 20.4C): The reduction of an imine or oxime derivative of a ketone or aldehyde to an amine.

Reflux (Lab 5.4): A method that heats a mixture containing a liquid solvent in a reaction vessel, which is connected to a condenser so that the vapors condense and fall back into the vessel.

Reflux Ratio (Lab 4.4): The ratio of the amount of condensate returning to the stillpot and the amount of vapor removed as distillate per unit time; the higher the reflux ratio, the more efficient the fractional distillation.

Reformatsky Reaction: Condensation of aldehydes or ketones with organozinc derivatives of α-halo esters to yield β-hydroxy esters: R₂C=O + BrCH₂CO₂R + Zn → HOCH₂CH₂CO₂R

Regioselective reaction (Sec 8.2C, 8.18): A reaction that yields only one (or a predominance of one) constitutional isomer as the product, when two or more constitutional isomers are possible.

Relative configuration (Sec 5.15A): Two different chiral molecules in which similar or identical groups in each occupy the same position in space.

Relative ratio of integrated peaks (Sec 9.2B, Lab 8.3): In ¹H NMR, the ratio of the heights of the integration steps is multiplied by a whole number to give a ratio of integers, which is the relative number of hydrogen atoms represented by each signal.

Resolution (Sec 5.16B, 20.3F): The process by which the enantiomers of a racemic mixture are separated.

Resonance effect (Sec 3.l1A, 13.5, l5.10, l5.11): An effect by which a substituent exerts either an electron-donating or electron-withdrawing effect through the pi system of the molecule.

Resonance energy (Sec 13.2, 13.4, 14.5): The energy of stabilization that represents the difference in energy between the actual molecule or ion and that calculated for any resonance structure; this lower energy state arises from delocalization of electrons, and it results in resonance stabilization.

Resonance stabilization (Sec 1.8, 13.2, 13.4, 14.5): The extra stability of a molecule that has resonance contributors, since the energy of the actual molecule is lower than the energy that is estimated for any of its resonance structures.

Resonance structures (Sec 1.8, 13.2, 13.4): Lewis structures of the same molecule that differ only in the position of their electrons; a single resonance structure will not adequately represent a molecule, and the molecule is best represented as a hybrid of all of the resonance structures. Also called resonance contributors.

Retro-aldol reaction (Sec 19.4B): A base-catalyzed conversion of an aldol into an aldehyde (and/or ketone); the reverse of an aldol addition reaction.

Retrosynthetic analysis (Sec 7.15B, 8.20): A method for planning a synthesis that involves reasoning backward from the target molecule through various levels of precursors, and finally to the starting materials.

Reversed phase chromatography (Lab 6.3): A form of chromatography in which a nonpolar stationary phase (adsorbent) is used with a more polar mobile phase (eluting solvent), and nonpolar compounds bind much more tightly than polar compounds.

Ring flip (Sec 4.12, 4.13): The change in a cyclohexane ring (resulting from partial bond rotations) that converts one ring conformation to another. A chair-chair ring flip converts any equatorial substitutent to an axial substituent and vice versa.

Ring strain (Sec 4.10): The increased potential energy of the cyclic form of a molecule when compared to its acyclic form, which is caused mostly by angle strain and torsional strain.

Robinson annulation (Sec 19.7B, Lab 18.4): Formation of a new six-membered ring, an α,β-unsaturated cyclic ketone, by the Michael addition of a cyclohexanone derivative to a methyl vinyl ketone derivative, followed by an intramolecular aldol condensation.

S

s Orbital (Sec 1.10): A spherical atomic orbital; the principal quantum number n ≥ 1; the azimuthal quantum number l = 0; the magnetic quantum number m = 0.

s-Cis conformation (Sec 13.11B): A cis-like conformation of a single bond in a conjugated diene or polyene.

s-Trans conformation (Sec 13.11B): A trans-like conformation of a single bond in a conjugated diene or polyene.

Salt (Sec 1.3A): An ionic compound composed of cations and anions; often formed by the reaction of an acid with a base.

Sandmeyer reaction (Sec 20.7B): Replacement of the -N≡N group in an arenediazonium salt by a cuprous salt; usually cuprous chloride, bromide, or cyanide.

Saponification (Sec 17.7B, 23.2C): Basic hydrolysis of an ester into an alcohol and a carboxylate salt.

Saturated compound (Sec 2.1, 7.12, 23.2): A compound that contains only single covalent bonds, and has the maximum number of hydrogen atoms that are possible.

Sawhorse projection (Sec 4.8): A structural formula indicating the spatial arrangement of bonds.

Schiff base (Sec 16.8A): A substituted imine, R₂C=NR'.

Secondary carbon (Sec 2.5): Carbon atom that has two other carbon atoms attached to it.

Secondary protein structure (Sec 24.1, 24.8): The local conformation of a polypeptide backbone. These local conformations are specified in terms of regular folding patterns such as β-pleated sheets, α-helixes, and turns.

Seeding (Lab 3.2): Adding crystals of the desired compound to the cold solution to induce crystallization.

Semicarbazone (Sec 16.8B): A compound containing the -C=N-NH-CONH₂ group, formed by the reaction of an aldehyde or ketone with semicarbazide, H₂NCONHNH₂ .

Shielding and deshielding of protons (Sec 9.7, Lab 8.3): Effects observed in ¹H NMR caused by different levels of magnetic shielding from the circulation of electrons within a chemical bond. Shielding causes signals to appear upfield (to the right) at smaller delta values, and at lower radio frequencies (or higher external magnetic fields). Deshielding causes signals to appear downfield (to the left) at larger delta values, and at higher radio frequencies (or lower external magnetic fields).

Sigma (σ) bond (Sec 1.12): A single bond formed when electrons occupy the bonding sigma orbital formed by the end-on overlap of atomic orbitals (or hybrid orbitals) on adjacent atoms. In a sigma bond, the electron density has circular symmetry when viewed along the bond axis.

Signal splitting (Sec 9.2C, 9.9, Lab 8.3): The ¹H NMR signal may be split into a multiplet by the magnetic effect of nonequivalent hydrogen neighbors separated by 2 or 3 bonds.

Simple Addition (Sec 13.10, 19.7): An addition reaction in which two groups add to adjacent atoms in a conjugated system, which is fast and under kinetic control; in α,β-unsaturated carbonyl compounds, a nucleophile adds to the carbonyl carbon and the carbonyl oxygen is protonated. Also called 1,2-addition.

Simple Distillation (Lab 4.3): A method that allows separation of distillates from non-volatile substances that remain as pot residue, or for separation of several volatile substances if their boiling points differ by greater than 40 °C.

Single bond (Sec 1.12): Chemical bond formed when two atoms share one pair of electrons by forming one sigma bond.

S_N1 reaction (Sec 6.9 - 6.13, 6.18, Lab 14): A multistep nucleophilic substitution reaction, in which the leaving group departs in a unimolecular step before the attack of the nucleophile; the rate equation is first order in substrate, but zero order in nucleophile. S_N1 stands for Substitution, Nucleophilic, Unimolecular.

S_N2 reaction (Sec 6.5 - 6.8, 6.13, Lab 14): A bimolecular nucleophilic substitution reaction that takes place in a single step (concerted reaction), in which a nucleophile attacks the carbon bearing a leaving group from the backside, which causes an inversion of configuration at this carbon and displacement of the leaving group. S_N2 stands for Substitution, Nucleophilic, Bimolecular.

Solid-liquid extraction (Lab 5.4): A method to remove a compound from a solid mixture, usually by refluxing the solid in a liquid organic solvent.

Sodium borohydride, NaBH₄ (Sec 12.3): A mild reducing agent that is usually used in an aqueous and/or alcohol solution; it reduces aldehydes and ketones into alcohols, but it will not reduce carboxylic acids or carboxylic derivatives, and it will not react with carbon-carbon double and triple bonds.

Solubility (Sec 2.13D): The amount of solute that can dissolve in a solvent at a given temperature; the like-dissolves-like rule states that polar molecules dissolve in polar solvents, and nonpolar molecules dissolve in nonpolar solvents.

Solute (Lab 3.2): The dissolved substance in a solution.

Solution (Lab 3.2): A homogeneous mixture of one or more substances (solutes) dispersed molecularly in a dissolving medium (solvent).

Solution recrystallization (Lab 3.2): A method to purify solid compounds involving selection of an appropriate solvent, dissolution of the solid in the solvent near its boiling point, decoloration with an activated form of carbon, filtration of the hot solution, formation of crystalline solid from the solution as it cools, isolation of the purified solid by filtration, and drying the crystals.

Solvent (Lab 3.2): A liquid that holds another substance in solution, i.e., dissolves it.

Solvent effect (Sec 6.l3): An effect on relative rates of reaction caused by the solvent; for example, the use of a polar aprotic solvent usually increases the rate of an S_N2 reaction, and the use of a protic solvent usually increases the rate of an S_N1 reaction.

Solvent selection for recrystallization (Lab 3.2): A desired compound is soluble in the hot solvent and nearly insoluble in the cold solvent, but impurities are either insoluble in the solvent at all temperatures or must remain at least moderately soluble in the cold solvent.

Solvolysis (Sec 6.12B): A nucleophilic substitution reaction in which the nucleophile is a molecule of the solvent; if the solvent is water, then the solvolysis is called a hydrolysis.

sp Orbital (Sec 1.14): A hybrid orbital that is derived by mathematically combining one s atomic orbital and one p atomic orbital; two sp hybrid orbitals are obtained by this process, and they are oriented in opposite directions with an angle of 180° between them.

sp² Orbital (Sec 1.13): A hybrid orbital that is derived by mathematically combining one s atomic orbital and two p atomic orbitals; three sp² hybrid orbitals are obtained by this process, and they are directed toward the corners of an equilateral triangle with angles of 120° between them.

sp³ Orbital (Sec 1.12A): A hybrid orbital that is derived by mathematically combining one s atomic orbital and three p atomic orbitals; four sp³ hybrid orbitals are obtained by this process, and they are directed toward the corners of a regular tetrahedron with angles of 109.5° between them.

Specific rotation, [α] (Sec 5.8C): A standardized measurement of the observed rotation of plane-polarized light by an optically active compound; [α] = α / ( c ∙ l ), where α is the observed rotation, c is the concentation in g/mL, and l is the pathlength in dm.

Spectroscopy (Sec 2.15, 9.1, 13.8, Lab 8): The study of the interaction of energy with matter, which can be used to elucidate the structure of a molecule.

Spin decoupling (Sec 9.10): An effect that causes spin-spin splitting not to be observed in ¹H NMR spectra.

Spin-spin coupling (Sec 9.9, Lab 8.3): The magnetic effect that produces signal splitting in ¹H NMR spectra. Vicinal coupling occurs between heterotopic hydrogen atoms that are bound to adjacent atoms and are separated by three sigma bonds. Geminal coupling occurs between diastereotopic hydrogen atoms that are bound to the same atom and are separated by two sigma bonds.

Spin-spin splitting (Sec 9.9B, Lab 8.3): An effect observed in NMR spectra that results in a signal appearing as a multiplet (i.e., doublet, triplet, quartet, etc.), which is caused by magnetic couplings of the nucleus being observed with the nuclei of nearby atoms.

Staggered conformation (Sec 4.8): A temporary orientation of groups around two atoms joined by a single bond such that the bonds of the back atom exactly bisect the angles formed by the bonds of the front atom in a Newman projection formula.

Standard deviation: A measure of precision; the variation of a set of values about the mean, calculated as the square root of the sum of the squares of the deviations from the mean for each value divided by one less than the number of values.

States of matter: The four physical forms that matter can assume: solid, liquid, gas, or plasma. Also called phases of matter.

State function (Sec 10.2): A property of a system that depends only on its present state, which is determined by variables such as temperature and pressure, and is independent of any previous history of the system.

Step-growth polymer (Sec 17.12): A polymer produced when bifunctional monomers react with each other through the intermolecular elimination of water or an alcohol. Examples are polyesters, polyamides, and polyurethanes. Also called a condensation polymer.

Stereochemistry (Sec 5.2, 6.8, 6.14): Chemical studies that take into account the spatial aspects of molecules.

Stereogenic center (Sec 5.4): An atom at which an interchange of groups produces a stereoisomer. Also called stereocenter.

Stereoisomers (Sec 1.13B, 4.9A, 4.13, 5.1 - 5.16): Compounds with the same molecular formula and the same connectivity, but are not superposable because they differ in the arrangement of their atoms in three-dimensional space; includes enantiomers and diastereomers, but excludes constitutional isomers.

Stereoselective reaction (Sec 5.10B, 8.21C, 12.3D): A reaction that produces a preponderance of one stereoisomer, where a stereogenic center is altered or created; an enantioselective reaction produces a preponderance of one enantiomer over the other; a diastereoselective reaction produces a preponderance of one diastereomer over the other.

Stereospecific reaction (Sec 8.12, 8.20C): A reaction in which a particular stereoisomeric form of the reactant can reacts in such a way that it leads to a specific stereoisomeric form of the product.

Steric effect (Sec 6.13A): An effect on the relative rate of reaction caused by the spatial arrangement of atoms at the reacting site.

Steric hindrance (Sec 4.8, 6.13A): (1) The interference between two groups when they come so close together that they produce Van der Waals repulsions. (2) A decrease in the relative rate of reaction caused when the spatial arrangement of atoms or groups at or near the reacting site hinders or retards a reaction.

Steric strain (Sec 4.8, 4.12): The interference between two groups when they come so close together that they produce Van der Waals repulsions.

Steroid (Sec 23.4): Lipids that are derived from a perhydrocyclopentanophenanthrene ring system.

Stretching vibrational mode (Sec 2.15, Lab 8.2): Regular, repetitive motion between two atoms connected by a covalent bond, in which the bond length changes; stretching vibrations are one type of molecular motion that gives rise to a peak in the infrared spectrum.

Stork enamine reaction (Sec 18.9): Synthesis of an α-alkyl or α-acyl carbonyl compound from the reaction of an enamine with an alkyl or acyl halide.

Stretching vibrations: Motions of two atoms in a molecule that take place along the bond axis, due to absorption of IR light; the IR absorption frequency decreases with increasing atomic mass, and the frequency increases with increasing bond energy.

Structural formula (Sec 1.7): Formula that shows how atoms of a molecule are attached to each other.

Structural theory of organic chemistry: The atoms in organic compounds can form a fixed number of bonds using their valence electrons (carbon is tetravalent, nitrogen is trivalent, oxygen is divalent, hydrogen is monovalent, halogens are usually monovalent, etc.). A carbon atom can use one or more of its valence electrons to form bonds to other carbon atoms.

Substituent effect (Sec 3.10D, 15.11F): An effect on the rate of reaction (or on the equilibrium constant) caused by the replacement of a hydrogen atom by another atom or group; effects include those caused by the size of the atom or group, called steric effects, and those effects caused by the ability of the group to withdraw or donate electron density, called electronic effects (inductive effects or resonance effects).

Substitution reaction (Sec 3.13, 6.2, 10.3, 15.1, 17.4 ): A reaction in which an atom or group in a compound is replaced by a different atom or group.

Substitutive nomenclature (Sec 4.3F): A system for naming compounds in which each atom or group, called a substituent, is cited as a prefix or suffix to a parent compound. In the IUPAC system, only one group may be cited as a suffix. Locants (usually numbers) are used to tell where the group occurs.

Substrate (Sec 6.2, 24.9): The reactant that is considered to be attacked in a chemical reaction.

Sugar (Sec 22.1, 22.12): A carbohydrate.

Sulfate ester (Sec 11.11): An alcohol derivative with the formula ROSO₂OR' , in which alkyl groups replace both hydrogen atoms in sulfuric acid, HOSO₂OH.

Sulfonamide (Sec 20.9): An amide of a sulfonic acid, which is the nitrogen analogue of a sulfonate ester.

Sulfonate ester (Sec 11.10): An alcohol derivative with the formula RSO₂OR' , containing one carbon atom bound to sulfur, and another carbon bound to an oxygen atom; the most common sulfonate esters are mesylates, tosylates, and triflates.

Sulfonation (Sec 15.5): Replacement of a hydrogen atom by a sulfonic acid group, -OSO₂H.

Superimposability of IR spectra (Sec 2.16, Lab 8.2): If the intensity, shape and location of every absorption in two IR spectra are the same, then there is a high probability that the two compounds are the same.

Superposable (Sec 1.13B, 5.1): Two objects that can be placed on top of each other so that all parts of each coincide. Also called superimposable.

Syn addition (Sec 7.13A, 8.6, 8.8, 8.15): An addition reaction that places both parts of the adding reagent on the same face of the reactant.

Syn coplanar (Sec 7.6D): The five atoms involved in the transition state of an E2 reaction must be coplanar, for proper overlap of orbitals in the developing pi bond of the alkene that is being formed. The syn coplanar transition state occurs only with rigid molecules that are unable to assume the more stable anti coplanar arrangement, because the base and leaving group are syn (eclipsed), and they directly oppose each other.

Syn 1,2-Dihydroxylation (Sec 8.16, 11.15): A syn addition reaction in which an oxidizing agent, such as osmium tetroxide, OsO₄ , adds two hydroxyl groups, -OH, to the same side of adjacent doubly bonded carbon atoms in alkenes to produce 1,2-diols (glycols); cycloalkenes will oxidize into cis-1,2-cycloalkanediols.

Syndiotactic polymer: A polymer in which the configuration at the stereogenic centers along the chain alternate regularly, i.e., (R), (S), (R), (S), etc.

Synthetic equivalent (Sec 8.20B, 18.6, 18.7): A reagent whose structure, when incorporated into a product, appears to have originated from one type of precursor, when as a reactant it actually had a different origin. For example, the ethyl acetoacetate enolate ion serves as the synthetic equivalent of the acetone enolate ion, and the diethyl malonate enolate ion serves as the synthetic equivalent of the ethyl acetate enolate ion.

Synthon (Sec 8.21B): The fragments that result (on paper) from the disconnection of a bond; the actual reagent that will provide the synthon, in a synthetic step, is called the synthetic equivalent.

T

Tautomerization (Sec 18.2, Lab 18.1): Process by which two isomers are interconverted by the movement of an atom or a group (usually a hydrogen atom); in the presence of an acid or base, keto and enol tautomers are in equilibrium: RCH₂COR' ↔ RCH=C(OH)R'. Also called tautomerism.

Tautomers (Sec 18.2): Constitutional isomers that are easily interconverted; keto and enol tautomers differ in the position of a hydrogen atom and are rapidly interconverted in the presence of an acid or base.

Temperature coefficient of a solvent (Lab 3.2): The fractional change in solubility per degree rise in temperature. A favorable temperature coefficient is when the desired compound is reasonably soluble in the hot solvent and nearly insoluble in the cold solvent.

Temperature gradient (Lab 4.4): The difference in temperature between the top and bottom of a distillation column.

Terpene (Sec 23.3): Terpenes are lipids that have a structure that can be derived on paper by linking isoprene units.

Tertiary carbon (Sec 2.5): Carbon atom that has three other carbon atoms attached to it.

Tertiary protein structure (Sec 24.1, 24.8): The three-dimensional shape of a protein that arises from folding of its polypeptide chains due to interactions between the side groups (R-groups) of the amino acids.

Tetramethylsilane (Sec 9.7, Lab 8.3): An inert, volatile liquid that is added to samples as an internal standard for ¹H NMR and ¹³C NMR. (CH₃)₄ Si has 12 homotopic hydrogens that are highly shielded, and 4 chemically equivalent carbons; therefore, only one large peak occurs higher upfield than most organic compounds, and it's chemical shift is defined as 0.000 ppm. Also called TMS.

Thermodynamics: Study of the energies of molecules.

Thermodynamic control (Sec 13.9A, 18.4A): A principle stating that the ratio of products of an equilibrium reaction is determined by the relative stabilities of the products, as measured by their standard free energies, ΔG°, and the most abundant product will be the one that is the most stable. Also called equilibrium control.

Thermodynamic enolate (Sec 18.4A, 19.5B): The most stable enolate formed from an unsymmetrical ketone, which has the more highly substituted double bond; it is favored by use of a protic solvent with a base that is weaker than the enolate ion, such as hydroxide ion or alkoxide ion, so that equilibrium can be established.

Thermodynamic product (Sec 13.9A): The most stable product; the major product under thermodynamic control.

Thioacetal (Sec 16.7D): A derivative of an aldehyde or ketone having two alkylthiol groups, -SR, in place of the carbonyl group, which is derived by adding two molar equivalents of a thiol.

Thiol (Sec 16.7D, Special Topic D): A molecule containing a sulfhydryl (mercapto) group, -SH, which is the sulfur analogue of an alcohol. Also called a mercaptan.

Thiol ester: An acid derivative in which the hydroxyl group of the acid is replaced by a sulfur atom and its attached alkyl or aryl group; it is a composite of a carboxylic acid and a thiol. Also called a thioester.

Tollens test (Sec 16.12B, Lab 25.7C): A test for aldehydes and α-hydroxy ketones. Adding the Tollens reagent, Ag(NH₃)₂OH, which is a silver-ammonia complex, will give a carboxylate salt and a silver mirror on the inside of a glass container.

Torsional barrier (Sec 4.8): The energy barrier to free rotation about single bonds in a molecule.

Torsional strain (Sec 4.8, 4.10): The resistance to twisting about a single bond, which is caused by breaking the favorable orbital overlap that stabilizes a conformation by hyperconjugation, and/or by eclipsed atoms coming so close together that they produce Van der Waals repulsions.

Tosylate (Sec 11.10): A p-toluenesulfonate ester (ester of an alcohol with para-toluenesulfonic acid); the tosylate group is an excellent leaving group.

trans- (Sec 1.13B, 4.5, 4.13, 5.2): Stereochemical prefix indicating that two substituents are on opposite sides of a double bond or ring.

Transesterification (Sec 17.7A): Substitution of one alkoxy group for another in an ester, which can take place under either acidic or basic conditions.

Transition state (Sec 6.6, 6.7, 6.10, 7.6, Lab 14): The unstable species, with a very brief existence, that occurs at a state of maximum potential energy, and shown on a potential energy diagram at an energy maximum. Also called activated complex.

Transmittance (Sec 2.15, 13.9): In a spectrometer, the amount of light transmitted through a sample divided by the amount of light transmitted through air; percent transmittance converts the fraction into a percent: %T = ( I / I₀ ) ∙100, where I₀ is the intensity of light entering the sample at a particular wavelength, and I is the intensity of light exiting the sample at the same wavelength. The smaller the value of %T, the greater the amount of radiation that is absorbed by the sample.

Triflate (Sec 11.10): A trifluoromethanesulfonate ester (ester of an alcohol with trifluoromethanesulfonic acid); the triflate group is an excellent leaving group.

Triple bond (Sec 1.3B): Chemical bond formed when two atoms share three pairs of electrons by forming one sigma bond and two pi bonds.

U

Ultraviolet spectrum: The portion of the electromagnetic spectrum in the wavelength range 100 – 380 nm, which is divided into the short wave UVC at 100 – 280 nm, the medium wave UVB at 280 – 315 nm, and the long wave UVA at 315 – 380 nm. UVC is the most dangerous and the most carcinogenic. UVB can cause sunburn and increase the risk of skin cancer. UVA is the least harmful and does not cause sunburn.

Ultraviolet-Visible Spectroscopy (Sec 13.8): A type of optical spectroscopy that measures the absorption of light in the visible and ultraviolet regions of the spectrum; UV-Vis spectra primarily provide structural information about the conjugation of multiple bonds in the compound being analyzed. Also called UV-Vis Spectroscopy.

Umpolung (Sec 19.7): A reversal of polarity of a carbonyl carbon atom in the alkylation of 1,3-dithianes.

Unimolecular reaction (Sec 6.9): A reaction whose rate-determining step involves only one chemical species.

Unsaturated compound (Sec 2.1, 7.12, 23.2): A compound that contains double or triple covalent bonds, has fewer than the maximum number of hydrogen atoms, and is capable of reacting with hydrogen under the proper conditions.

Upfield (Sec 9.3, Lab 8.3): The right side of a NMR spectrum where shielded nuclei absorb, at smaller delta values, and at lower radio frequencies (or higher external magnetic fields, which is "up the field").

Urea (Sec 17.9): An organic compound that is the diamide of carbonic acid, H₂NCONH₂ , with two amine groups, -NH₂ , joined to a carbonyl group, >C=O . Also called carbamide

Urethane (Sec 8.9A): An ester of a carbamic acid, RNH-COOR. Also called a carbamate ester.

V

Vacuum filtration (Lab 3.2): Use of a partial vacuum to rapidly filter a mixture through a Buchner funnel.

Valence electrons (Sec 1.3): Electrons in the outermost shell of an atom that take part in its chemical reactions.

Valence shell electron pair repulsion theory (Sec 1.16): A model for predicting the shapes of molecules and ions in which valence electron pairs are arranged around each atom to minimize the repulsion of electron pairs by maximizing the distance between them. Abbreviated VSEPR.

Van der Waals forces (Sec 2.13B, 4.7): All of the intermolecular forces that do not involve cations, anions or covalent bonds, such as the forces of permanent dipoles, hydrogen bonds, induced dipoles, and electron clouds.

Van der Waals repulsions (Sec 4.9 - 4.11): Repulsive forces between atoms produced when the van der Waals surface of one atom is penetrated by that of another atom, which causes strong repulsive forces between the overlapping electron clouds. Also called repulsive dispersion forces.

Van der Waals surface (Sec 1.12, 2.2A): A plot of the furthest extent of a molecule's electron cloud, and thus its overall shape; when the van der Waals surface is penetrated by another molecule, it experiences strong repulsive forces between the overlapping electron clouds.

Vicinal (vic-) (Sec 7.10): Substituents that are on adjacent atoms.

Vinyl group (Sec 4.5, 6.1): The common name for the ethenyl group, H₂C=CH─

Vinylic halide (Sec 6.1): An organic halide in which the halogen atom is attached to a carbon atom of a C=C double bond. Also called alkenyl halide or haloalkene.

Vinylic substituent (Sec 6.1): Refers to a substituent on a carbon atom that participates in a carbon-carbon double bond.

Visible spectrum: The portion of the electromagnetic spectrum in the wavelength range 380 – 760 nm, where light is visible to the human eye. The seven most obvious colors in a rainbow are violet, indigo, blue, green, yellow, orange and red.

W

Water solubility (Sec 2.13E, Lab 25.3B): An organic compound is water soluble if at least 3 g of the compound dissolves in 100 mL of water, or at least 30 mg dissolves in 1 mL of water (3 % m/V). Organic compounds with one hydrophilic group per three carbon atoms are usually water soluble.

Wave function ( ψ function) (Sec 1.9): A mathematical expression derived from quantum mechanics corresponding to the energy state for an electron in its orbital. The square of the ψ function, ψ², gives the probability of finding the electron in a given region of space.

Wavelength, λ (Sec 2.16, 9.2, 13.9, Lab 8): The distance between consecutive peaks (or troughs) of a wave; often expressed in μm; the product of the wavelength and the frequency is the speed of light: c = λ ∙ υ where c = 2.99792458 × 10⁸ m/s.

Wavenumber (Sec 2.15, Lab 8.2): The frequency of a wave, expressed as the number of wavelengths that fit into one centimeter; often expressed in cm^-l ; the product of the wavenumber (in cm^-l ) and the wavelength (in μm) is 10,000.

Wilkinson’s catalyst (Sec 7.13): A homogenous hydrogenation catalyst, Rh[(C₆H₅)₃P]₃Cl.

Williamson ether synthesis (Sec 11.11B, 21.6): Synthesis of an unsymmetrical ether by alkylation of an alkoxide anion, RO^-, with a primary alkyl halide, R' X (or with an alkyl sulfate or alkyl sulfonate), which reacts by an S_N2 mechanism: RO^- + R' X → ROR' + X^-

Wittig reaction (Sec 16.10): Reaction of an aldehyde or ketone with a phosphorus ylide to form an alkene.

Y

Ylide (Sec 16.10): An electrically neutral molecule that has a negative carbon, with a lone pair of electrons, adjacent to a positive heteroatom.

Z

Zaitsev's rule (Sec 7.6B, 7.8A): The major product of an elimination reaction will be the most stable alkene, which has the most highly substituted double bond.

Zwitterion (Sec 24.2C): The charge-separated form of an amino acid that results from the transfer of a proton from a carboxyl group to a basic group. Also called a dipolar ion.

References:

(1) Solomons, T. W. Graham and Fryhle, Craig B., 2014, Organic Chemistry, 11th Edition, Wiley.

(2) Gilbert, John C. and Martin, Stephen F., 2011, Experimental Organic Chemistry: A Miniscale and Microscale Approach, 5th Edition, Thomson, Brooks/Cole.

(3) Wade, Leroy G., 2013, Organic Chemistry, 8th Edition, Pearson, Prentice Hall.

(4) McMurry, John E., 2012, Organic Chemistry, 8th Edition, Thomson, Brooks/Cole.

(5) Brown, William H., Foote, Christopher S., Iverson, Brent L. and Anslyn, Eric V., 2012, Organic Chemistry, 6th Edition, Brooks/Cole, Cengage.

(6) Bruice, Paula Y., 2011, Organic Chemistry, 6th Edition, Pearson, Prentice Hall.

(7) Carey, Francis A., 2011, Organic Chemistry, 8th Edition, McGraw Hill.

(8) The Merck Index, 2006, 14th Edition, Merck & Co., Inc.

(9) CRC Handbook of Chemistry and Physics, 2007, 87th Edition, CRC Press LLC.

(10) NIST Chemistry WebBook, NIST Standard Reference Database, Number 69, 2008, Eds. P.J. Linstrom and W.G. Mallard, National Institute of Standards and Technology, http://webbook.nist.gov/chemistry/