carboxyl group (-COOH)
The carboxyl group is the -COOH functional group, and is found in all carboxylic acids and amino acids. It consists of a carbon atom joined by covalent bonds to two oxygen atoms, one of which in turn is covalently bonded to a hydrogen atom. One valence electron on the carbon is available for bonding to another atom so that the carboxyl group can form part of a larger molecule. A carboxyl group is a carbonyl group attached to a hydroxyl group.