Which functional group characterizes carboxylic acids?

Carboxylic acids are characterized by the presence of the carboxyl functional group, which is denoted by the formula -COOH. This group consists of a carbon atom double-bonded to an oxygen atom (carbonyl) and also bonded to a hydroxyl group (-OH). The presence of both these features defines a compound as a carboxylic acid.

The -COOH group is responsible for the typical acidic properties of carboxylic acids, as it can donate a proton (H+) in an aqueous solution, leading to the establishment of equilibrium with its conjugate base. This acidic behavior is a fundamental characteristic that distinguishes carboxylic acids from other organic compounds.

Other functional groups listed, such as -NH2 (amine), -OH (alcohol), and -CHO (aldehyde), define different classes of organic compounds and do not confer the specific acidic nature associated with carboxylic acids. Hence, the correct identification of -COOH as the defining functional group for carboxylic acids is crucial in organic chemistry nomenclature and classification.