Nomenclature

Common Names

Because carboxylic acids were among the very first organic compounds ever isolated, many of them are still known chiefly by their traditional, non-systematic names. These common names share a giveaway pattern: they all end in the suffix -ic acid, and the name itself is usually borrowed from the Latin or Greek word for the natural source the acid was first obtained from.

A few classic examples make the pattern clear:

• Formic acid, $\text{HCOOH}$ — first obtained from red ants (Latin formica, meaning ant).
• Acetic acid, $\text{CH}_3\text{COOH}$ — obtained from vinegar (Latin acetum, meaning vinegar).
• Butyric acid, $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ — obtained from rancid butter (Latin butyrum, meaning butter).

IUPAC Names

The systematic name is built from the corresponding alkane in a simple two-step swap: drop the final -e of the alkane's name and replace it with the suffix -oic acid.

When numbering the carbon chain to place substituents, the carboxylic carbon is always taken as carbon 1 — it gets the lowest possible locant by convention, since it anchors the parent chain.

Naming acids with more than one carboxyl group. When a compound carries two or more $-\text{COOH}$ groups, the numbering strategy changes slightly:

1. Number the alkyl chain that is left over once the carboxyl groups are set aside.
2. Show how many carboxyl groups are present using a multiplying prefix on the parent name — dicarboxylic acid, tricarboxylic acid, and so on. …