Benzenediols or dihydroxybenzenes are organic chemical compounds in which two hydroxyl groups are substituted onto a benzene ring. These aromatic compounds are classed as phenols. There are three isomers of benzenediol: 1,2-benzenediol (the ortho isomer) is commonly known as catechol, 1,3-benzenediol (the meta isomer) is commonly known as resorcinol, and 1,4-benzenediol (the para isomer) is commonly known as hydroquinone.