The unconventional CnHn empirical formula of benzene proved to be a great challenge for chemists. Kekule put forth the correct structure in 1865. According to him,benzene has an aromatic structure. This structure met with lot of criticism in the beginning and was further refined. The only way in which this could be explained is pi bonds in the aromatic ring.
Benzene is the most common aromatic hydrocarbon. The benzene molecule has six carbon atoms connected in a ring. Each carbon atom has four bonding sites available however in benzene three are used and one is free. The three bonds are covalent the fourth can be shared by all six carbon atoms.