Kekule suggested that benzene consists of a cyclic planar structure of six carbon with alternate single and double bonds.
There were two objections:
1. Benzene forms only one ortho disubstituted products whereas the Kekule’s structure predicts two ortho disubstituted products as shown:
2. Kekule’s structure failed to explain why benzene with three double bonds did not give addition reaction like alkenes. To overcome this objection, Kekule suggested that henzene was a resonance hybrid of two forms(1 and 2) which are in rapid equilibrium.