The carboxyl group, R-COOH, is one of the most common and important organic functional groups. Chemicals that contain the carboxyl group belong to the large family of organic compounds that contain the carbonyl group, C=O, a carbon atom doubly bonded to an oxygen atom. The carboxyl group consists of a carbonyl group whose carbon atom is singly bonded to a hydroxyl group, -OH. The carboxyl group carbon atom also makes a bond to a carbon atom within the main chain of the parent compound. Some familiar compounds which contain a carboxyl group are acetic acid (the main component of vinegar), formic acid (the compound responsible for the "sting" of various ants and plant nettles), amino acids (the "building blocks" of every protein), and butyric acid (the chemical responsible for the stench of rancid butter).

The carboxyl group is sp² hybridized and as a result has...