Benzene and derivatives are aromatic hydrocarbons with one ring or several rings fused together. The aromatic character of benzene and derivatives have special stability, which imparts a unique chemical profile. The delocalized bonding in benzene is not properly described by a structure that shows localized single and double bonds. Two structures are needed to properly represent benzene, with a double-headed arrow to show they are resonance contributors. In benzene derivatives one or more hydrogen atoms have been replaced with alkyl groups, heteroatom substituents, or functional groups. Dimethylbenzene is an arene with two substituents on the ring and has the common name xylene.