An organic aci is an organic compound with acidic properties. The most common organic acids are the carboxylic acids whose acidity is associated with their carboxyl group -COOH. Sulfonic acids, containing the group OSO3H, are relatively stronger acids. The relative stability of the conjugate base of the acid determines its acidity. Other groups can also confer acidity, usually weakly: -OH, -SH, enol group, and the phenol group. In biological systems organic compounds containing only these groups are not generally referred to as organic acids.