20.2: Naming Carboxylic Acids and Nitriles

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Carboxylic Acids, RCO₂H

Simple carboxylic acids derived from open-chain alkanes are systematically named by replacing the terminal –e of the corresponding alkane name with -oic acid. The –CO₂H carbon atom is numbered C1.

The structures of propanoic acid, 4-methylpentanoic acid, and 3-ethyl-6-methyloctane dioic acid. The carbon atoms are numbered and substituents are highlighted.

Compounds that have a –CO₂H group bonded to a ring are named using the suffix -carboxylic acid. The CO₂H carbon is attached to C1 in this system and is not itself numbered. As a substituent, the CO₂H group is called a carboxyl group.

The structures of trans-4-hydroxycyclohexanecarboxylic acid and 1-cyclopentenecarboxylic acid. The carbon atoms in both structures are numbered.

Because many carboxylic acids were among the first organic compounds to be isolated and purified, quite a few common names exist (Table 20.1). Biological chemists, in particular, make frequent use of these names, so you may find yourself referring back to this list on occasion. We’ll use systematic names in this book, with a few exceptions such as formic (methanoic) acid and acetic (ethanoic) acid, whose names are accepted by IUPAC and are so well known that it makes little sense to refer to them any other way.

Also listed in Table 20.1 are the names of acyl groups The structure of the acyl group where C is double bonded to an O and single bonded to R and any other atom. derived from the parent acids. Except for the eight entries at the top of Table 20.1, whose names have a -yl ending, all other acyl groups are named using an -oyl ending.

Table 20.1 Common Names of Some Carboxylic Acids and Acyl Groups
Structure	Name	Acyl group
HCO₂H	Formic	Formyl
CH₃CO₂H	Acetic	Acetyl
CH₃CH₂CO₂H	Propionic	Propionyl
CH₃CH₂CH₂CO₂H	Butyric	Butyryl
HO₂CCO₂H	Oxalic	Oxalyl
HO₂CCH₂CO₂H	Malonic	Malonyl
HO₂CCH₂CH₂CO₂H	Succinic	Succinyl
HO₂CCH₂CH₂CH₂CO₂H	Glutaric	Glutaryl
HO₂CCH₂CH₂CH₂CH₂CO₂H	Adipic	Adipoyl
H₂C═CHCO₂H	Acrylic	Acryloyl
HO₂CCH═CHCO₂H	Maleic (cis) Fumaric (trans)	Maleoyl Fumaroyl
HOCH₂CO₂H	Glycolic	Glycoloyl
	Lactic	Lactoyl
	Pyruvic	Pyruvoyl
	Glyceric	Glyceroyl
	Malic	Maloyl
	Oxaloacetic	Oxaloacetyl
	Benzoic	Benzoyl
	Phthalic	Phthaloyl

Nitriles, $RC≡N$

Compounds containing the $–C≡N$ functional group are called nitriles and can undergo some chemistry similar to that of carboxylic acids. Simple open-chain nitriles are named by adding -nitrile as a suffix to the alkane name, with the nitrile carbon numbered C1.

The structure of 4-methylpentanenitrile. C 1 belongs to the C N group. A methyl group is attached to C 4. All the carbon atoms are numbered.

Nitriles can also be named as derivatives of carboxylic acids by replacing the -ic acid or -oic acid ending with -onitrile, or by replacing the -carboxylic acid ending with -carbonitrile. The nitrile carbon atom is attached to C1 but is not itself numbered.