A common carboxylic acid is ethanoic acid, vinegar. Carboxylic acids are weak acids that react in the same way as other acids. They are responsible for the rancid flavour and smell of off food.

Carboxylic acids can undergo reduction reactions. Reduction is the opposite of oxidation. For example, ethanoic acid (CH 3 COOH) can be formed by the oxidation of ethanol as shown below.

an 18-carbon saturated fatty acid. The normal numbering system, starting with the carboxylic acid, is shown in blue. The carbons and oxygens of the carboxylic acid functional group are red.