Carboxylic acid

A functional group with the general structure RC(O)–OH.  Loss of a proton (H+) from a carboxylic acid results in its resonance-stabilized conjugate base, called a carboxylate.  Common examples of carboxylic acids are acetic acid (CH₃COOH, pK_a = 4.7) and benzoic acid (C₆H₅COOH, pK_a = 4.2).