Benzene (C6H6) is the most well known aromatic hydrocarbon. It is a sweet smelling highly inflammable liquid boiling at 80.1 degrees centigrade. The extraordinary stability of benzene is attributed to widespread resonance in its ring structure which is represented by a six-membered ring with three alternate double bonds. The resonance representation accounts for unusually high amount of resonance energy (36.0 Kcal/mole)of benzene molecule. This model also accommodates well its observed structural peculiarity of equality of all the C – C bond distances (1.397) Å. All other aromatic hydrocarbons are obtainable from benzene, hence called derivatives of benzene.