13.1: IUPAC Nomenclature of Carboxylic Acids
IUPAC names of carboxylic acids are systematically derived following a few rules discussed below.
For acyclic saturated monocarboxylic acids, the longest hydrocarbon chain containing the –COOH carbon is identified as the parent chain. Then, the last -e of the parent hydrocarbon name is replaced with a suffix -oic acid.
Numbering the parent carbon chain is performed starting from the –COOH carbon. The names and positions of the substituent are then listed alphabetically as a prefix to the parent name. Some examples are given below:
It is to be noted that all other functional groups like -CHO, -CO-, -OH, -OR, -NH2, and halogens are given less priority over the –COOH group, and thus they are treated as substituents in the presence of –COOH groups.
Unsaturated carboxylic acids are named after the parent alkene or alkyne. The position of multiple bonds is indicated by a locant prefixed to the parent alkene or alkyne. The cis/trans or E/Z notations are prefixed to the parent alkene to indicate the stereochemistry around the double bond.
Acyclic dicarboxylic acids have similar nomenclature rules, except that the terminal -e of the parent hydrocarbon is retained, and a suffix -dioic acid is added.
Compounds containing more than two –COOH groups are sometimes named by treating one of them as a substituent. For example, the carboxylic acid shown below treats the –CH2COOH group as a substituent and uses the prefix carboxymethyl- to the parent name.
In the case of cyclic carboxylic acids having –COOH groups directly attached to a cycloalkane ring or an aromatic ring, a suffix -carboxylic acid is added to the parent ring name. However, unlike acyclic carboxylic acids, the ring carbon attached to the –COOH group is numbered as carbon-1.