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.