Which functional group is characteristic of carboxylic acids?

Carboxylic acids are defined by the presence of the carboxyl functional group, which has the structure -COOH. This group consists of a carbon atom double-bonded to an oxygen atom (carbonyl, C=O) and single-bonded to a hydroxyl group (alcohol, -OH). The combination of these two elements is what characterizes carboxylic acids, providing them with unique properties such as acidity.

The characteristic -COOH group is essential for identifying carboxylic acids in organic chemistry, as it influences the reactivity and interactions of the compound. In contrast, the other functional groups mentioned do not define carboxylic acids: -OH denotes alcohols, -NH2 indicates amines, and -SH refers to thiols. Hence, the recognition of the -COOH group is crucial for differentiating carboxylic acids from other organic compounds.