A carboxyl group is a functional group in organic chemistry, consisting of a carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group (–OH). This structure is represented as –COOH and is characteristic of carboxylic acids, which are important in various biological and chemical processes. Carboxylic acids, such as acetic acid and citric acid, are commonly found in nature and play vital roles in metabolism. The presence of the carboxyl group makes these compounds acidic, allowing them to donate protons (H+) in solution, which is a key feature in many chemical reactions.