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Organic Chemistry
A. Precis of Modern Structure Theory
Valence refers to the number of bonds an atom can form with its neighbors. Organic chemists normally regard hydrogen and halogen atoms (fluorine, chlorine, bromine, and iodine) as monovalent, oxygen and sulfur as divalent, nitrogen and phosphorus as trivalent, and carbon atoms as tetravalent. These elements provide the building blocks for the large majority of all organic compounds. Following the valence rules, one can schematically construct organic compounds by linking the atoms together. The simplest organic compound is methane, CH4 ; the carbon atom is tetravalent and each of the hydrogen atoms is monovalent, so the rules are satisfied and the compound is stable. The first homolog (that is, next in the same chemical series) of methane is ethane, constructed by removing one of the four hydrogen atoms of methane (which produces a methyl radical, -CH3 , sometimes symbolized Me) and filling the vacant valence with another methyl group: H3 C-CH3 . Note that conditions of carbon tetravalence and hydrogen monovalence are still met.
Taking one hydrogen from each carbon atom of ethane will schematically construct ethylene, the simplest of the class of hydrocarbons known as olefins : H2 C=CH2 . Note that the two unoccupied valences on the two adjacent carbons may be considered to have linked with each other. Olefins by definition have at least one double bond between adjacent carbon atoms, so that each of these atoms has only two remaining valences for attachment to hydrogen atoms. Ethylene chloride results from the addition of a chlorine molecule, Cl2 , to ethylene, with the carbon-carbon double bond thus disappearing: . (Here the carbon atoms are understood to be bonded directly together, despite the fact that they are not written adjacently; there is no ambiguity if one remembers the valences.) An isomer of ethylene chloride is ethylidene chloride, CH3 CHCl2 . Isomers are compounds with the same overall formula but with different structures, which is to say, with different properties.
Substances containing only carbon and hydrogen (hydrocarbons ) are mostly fairly unreactive and chemically uninteresting compounds. In general, chemical interest is created by the introduction of heteroatoms , i.e., atoms other than carbon or hydrogen. The most common and important of these is oxygen. Heteroatoms, or any multiple bonds, tend to create chemically reactive sites within an organic molecule and are called functional groups . Most reactions center on such groups of atoms.
Some examples will help. If a hydrogen atom is removed from either carbon atom of ethane (creating ethyl, CH3 CH2 -, often symbolized Et) and is replaced by a hydroxyl radical, -OH, one obtains ethyl alcohol, CH3 CH2 OH. if one then extracts the remaining two hydrogens from the second carbon atom of alcohol and replaces them with one double-bonded oxygen atom, we have the formula for acetic acid, CH3 COOH. The -COOH or CO2 H group (O=C-OH, with one valence still remaining on the carbon atom) is known as carboxyl . An intermediate stage of oxidation between alcohol and acid is
aldehyde, CH3 HC=O; it is carboxyl without the second oxygen atom. Two carboxyl groups connected together (or, equivalently, acetic acid in which the three hydrogens attached to the first carbon atom are replaced by =O and -OH), is the simplest dibasic (i.e., double) organic acid, oxalic acid. It can be obtained by vigorous oxidation of acetic acid or alcohol. If the oxidation is done more carefully or indirectly, other functional groups can be introduced. Glycol has hydroxyl groups on both carbon atoms; it is a double alcohol. Glyoxal has two aldehyde groups on the two carbons, a double aldehyde. Glycolic acid, a hydroxy-acid, is acetic acid in which one of the hydrogens of the methyl group is replaced by hydroxyl, HOCH2 CO2 H. Analogous homologs can be created from the three-carbon hydrocarbon, propane, and from the three-carbon acid, propionic acid, CH3 CH2 CO2 H. Propionic acid with a hydroxyl group on the middle carbon is lactic acid; the trialcohol with a hydroxyl on each carbon atom is glycerin.
This gives only a sample of the richness of organic chemical formulas, but it accurately reflects the sort of schematic manipulations that characterize structural organic chemistry.
B. Modern Chemical Definitions[1]
acetic acid = essence of vinegar: CH3 CO2 H
acetoacetic ester: CH3 COCH2 CO2 CH2 CH3 , produced by self-condensation of ethyl acetate, CH3 CO2 CH2 CH3
acetone: CH3 COCH3 , the simplest ketone
acetyl: CH3 CO- (the oxygen is double bonded to carbon, which has an untilled valence)
acetylene : acid anhydride: acid from which the elements of water (H2 O) have been extracted
acid chloride: compound of the form RCOCl
alanine: CH3 CH(NH2 )CO2 H, aminopropionic acid
alcohol: loosely, a compound with a hydroxyl (-OH) group
aldehyde: any compound whose carbon chain ends in -CH=O
aldehyde (loosely) = acetaldehyde: CH3 CHO
aliphatic compound: non-benzenoid organic compound
alkyl: saturated hydrocarbon radical, often symbolized generically as "R"
amide: compound of the form RCONH2 (this particular example is a primary amide)
amine: compound of the form NR3 , where the R's are hydrogen or hydrocarbon groups
amino acid: compound with both amine and carboxylic acid groups
amyl: a five-carbon saturated hydrocarbon radical
amylene: a five-carbon olefin
aniline: C6 H5 NH2 , aminobenzene
anthranilic acid:ortho -aminobenzoic acid
aromatic compound: organic compound derived from benzene
-ate: suffix indicating ester or salt of an acid
benzaldehyde: C6 H5 CHO, benzoyl hydride
benzene: C6 H6
benzoic acid: C6 H5 CO2 H, benzenecarboxylic acid
benzonitrile: C6 H5 CN
benzoyl: C6 H5 CO-, phenyl carbonyl
benzyl alcohol: C6 H5 CH2 OH
butane: a four-carbon saturated hydrocarbon
butyl: a four-carbon saturated hydrocarbon radical
butylene: a four-carbon olefin
butyric acid: a four-carbon carboxylic acid
caproic acid: a six-carbon carboxylic acid
carbohydrate: a compound exhibiting a multiple of the formula CH2 O
carbonyl: functional group consisting of a carbon atom double bonded to oxygen
carboxyl: -COOH, confers acid character on a molecule
carboxylic acid: loosely, an organic acid, or a compound with a carboxyl group
chloroform: CHCl3
condensation: amalgamation of two molecules into one, often with loss of H2 O
cresol: methyl phenol, MeC6 H4 OH
cyanogen: NC-CN
cyclohexamethine: any proposed structure for benzene exhibiting a cyclical array of six trivalent CH groups
cyclohexatriene: Kekulé's hexagonal benzene formula, possessing three carbon-carbon double bonds and three carbon-carbon single bonds; an example of a cyclohexamethine theory
dibasic acid: acid having two replaceable hydrogen atoms; a double acid
dimer: compound formed of two identical parts, a "doubled" molecule
dithionic acid = hyposulfuric acid: H2 S2 O6
ester: compound of the form RCO2 R, resulting from condensation of an organic acid and an alcohol
ethane: CH3 CH3
ether: compound of the form R-O-R, where the R's are hydrocarbon radicals
ether (loosely) = diethyl ether: CH3 CH2 OCH2 CH3 or EtOEt
ethyl: CH3 CH2 -, often symbolized Et
ethyl alcohol = (loosely) alcohol: CH3 CH2 OH or EtOH
ethylamine: EtNH2
ethylene: CH2 =CH2 , the simplest olefin or alkene
ethylidene: CH3 CH= (a radical, or incomplete molecule)
fatty acid: large organic acids found as components of fats
formic acid: HCO2 H
functional group: any site on an organic molecule that has a multiple bond or a heteroatom
glyceride: ester of fatty acid(s) plus glycerin; triglycerides are fats
glycerin: CH2 OHCHOHCH2 OH, a trialcohol
glycine = glycocoll: aminoacetic acid
glycol: compound with two hydroxyl groups, a dialcohol
glycol (loosely) = ethylene glycol: CH2 OHCH2 OH
glycolic acid: CH2 OHCO2 H
glyoxal: OHCCHO
halide: chloride, bromide, iodide, or fluoride
halogen: chlorine, bromine, iodine, or fluorine
heteroatom: in an organic molecule, any atom other than hydrogen or carbon
homolog: a member of a homologous series
homologous series: series of organic compounds that differ only by successive CH2 (methylene) groups, each methylene representing a link in the carbon chain
hydracid: compound whose acidity is unconnected with its oxygen content
hydride: compound of the form X-H, where X may be almost any atom or radical
hydrocarbon: a compound consisting only of hydrogen and carbon
hydrolysis: reaction with water, often splitting the reactant molecule
hydroxyl: -OH, confers alcohol character
iso-: prefix indicating either (1) a new isomer of a familiar compound hitherto thought to have no isomers; or (2) a branched-chain hydrocarbon
isoamyl: Me2 CHCH2 CH2 -
isobutyl: Me2 CHCH2 -
isobutyric acid: Me2 CHCO2 H
isomers: compounds with the identical formula but different structures, that is, compounds that have the same sorts and numbers of atoms but arranged differently
isopropyl alcohol: CH3 CH(OH)CH3
ketone: compound of the form RCOR, that is, carbonyl flanked by two alkyl radicals
lactic acid: CH3 CH(OH)CO2 H
leucic acid: a six-carbon hydroxy acid
leucine: a six-carbon amino acid
malic acid: a four-carbon hydroxy diacid; hydroxysuccinic acid
malonic acid: HO2 CCH2 CO2 H, a three-carbon diacid
methane: CH4 , called "marsh gas" in the nineteenth century
methine: CH, a trivalent radical
methyl: CH3 -, often symbolized Me
methylamine: MeNH2
methylene: CH2 , a divalent radical
methylsulfonyl chloride: CH3 SO2 C1
methylsulfonic acid: CH3 SO3 H
moiety: organic-chemical term indicating a portion of a molecule
nitrile = cyanide: compound with the group -CN
normal: possessing a straight (unbranched) carbon chain, symbolized n -
octane: an eight-carbon saturated hydrocarbon
olefin: a hydrocarbon with a carbon-carbon double bond; alkene
ortho/meta/para: referring to aromatic isomers distinguished by virtue of two substituents occupying different positions on the benzene hexagon-on adjacent carbons (1,2), separated by one carbon (1,3), or on opposing carbons (1,4), respectively
oxalic acid: HO2 CCO2 H
oxyacid: compound whose acidity is related to its oxygen content
paraffin: a hydrocarbon with no multiple bonds; alkane
pentane: a five-carbon saturated hydrocarbon
phenol = carbolic acid: phenyl hydroxide or hydroxybenzene, C6 H5 OH
phenyl: C6 H5 -
phosgene = carbonyl chloride: COCl2
polymer: compound formed of many identical parts
primary alcohol or amine: compound of the form RCH2 OH or RNH2
propane: CH3 CH2 CH3
propionic acid: CH3 CH2 CO2 H
propyl =n-propyl = normal propyl: CH3 CH2 CH2 -
propylene: CH3 CH=CH2
salicylic acid:ortho -hydroxybenzoic acid
saturated: organic compound possessing no carbon-carbon multiple bonds
secondary alcohol or amine: compound of the form R2 CHOH or R2 NH
succinic acid: a four-carbon saturated dicarboxylic acid
sulfonic acid: a compound of the form RSO3 H
tartaric acid: a four-carbon dihydroxy diacid; dihydroxysuccinic acid
tertiary alcohol or amine: a compound of the form R3 COH or R3 N
tertiary butyl alcohol =t-butyl alcohol: Me3 COH
toluene: methylbenzene
unsaturated: possessing carbon-carbon multiple bonds (can absorb hydrogen gas)
valence: number of bonds a given kind of atom can form to other atoms
valeric acid: a five-carbon carboxylic acid