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Organic Chemistry

20.1 Naming Carboxylic Acids and Nitriles

Organic Chemistry20.1 Naming Carboxylic Acids and Nitriles

20.1 • Naming Carboxylic Acids and Nitriles

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
The structure of lactic acid, a propanoic acid with a hydroxyl group attached to C 2. Lactic Lactoyl
The structure of pyruvic acid (2-oxopropanoic acid). Pyruvic Pyruvoyl
The structure of glyceric acid (2,3-dihydroxypropanoic acid). Glyceric Glyceroyl
The structure of malic acid (2-hydroxybutanedioic acid). Malic Maloyl
The structure of oxaloacetic acid (oxobutanedioic acid). Oxaloacetic Oxaloacetyl
The structure of benzoic acid. A C O O H group is attached to the C 1 of the benzene ring. Benzoic Benzoyl
The structure of phthalic acid. Two C O O H groups are connected to the benzene ring's C 1 and C 2. Phthalic Phthaloyl

Nitriles, RC≡NRC≡N

Compounds containing the –C≡N–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.

The structures of acetonitrile (from acetic acid), benzonitrile (from benzoic acid), and 2,2-dimethylcyclohexanecarbonitrile (from 2,2-dimethylcyclohexane-carboxylic acid).

If another carboxylic acid derivative is present in the same molecule, the prefix cyano- is used for the C≡NC≡N group.

The structure of methyl-4-cyanopentanoate. Cyano group is attached to C 4. The C 1 is double-bonded to an O atom and single-bonded to the O C H 3 group.
Problem 20-1
Give IUPAC names for the following compounds:
The structure of 3-methylbutanoic acid, which has a C O O H group on C 1 and a methyl group on C 3 of a four-carbon chain.
The structure of 4-bromopentanoic acid, which has a C O O H group on C 1 and a bromine atom on C 4 of a five-carbon chain.
The structure of 2-ethylpentanoic acid, which has a C O O H group on C 1 and an ethyl on C 2 of a five-carbon chain.
The structure of (Z)-hex-4-enoic acid with six-carbon atoms. There is a C O O H on C 1, and C 4 and C 5 are double bonded with cis arrangement.
The structure of 2,4-dimethylpentane, which is a five-carbon chain in which C 1 is part of a C N group. There are methyl groups on C 2 and C 4.
The structure of cyclopentane-1,3-dicarboxylic acid with cyclopentane ring. There are C O O H groups on C 1 and C 3, positioned cis to each other.
Problem 20-2
Draw structures corresponding to the following IUPAC names:
2,3-Dimethylhexanoic acid
4-Methylpentanoic acid
trans-1,2-Cyclobutanedicarboxylic acid
o-Hydroxybenzoic acid
(9Z,12Z)-9,12-Octadecadienoic acid
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