A cyclic olefin with a carbon number of 4n+2 (n is a positive integer, benzene is n=1) and an alternating arrangement of single and double bonds is called an annulene, and benzene is a type of annulene. Benzene molecule is a planar molecule with 12 atoms in the same plane, 6 carbon and 6 hydrogen are equal, and the C-H bond length is 1.08 Α， C-C key length is 1.40 Α， This value is between the lengths of single and double bonds. All bond angles in the molecule are 120 °, and carbon atoms undergo sp2 hybridization. Each carbon atom still has a p-orbital perpendicular to the molecular plane, and each orbital has an electron. Six orbitals overlap to form a large delocalized π bond. According to the resonance hybridization theory proposed by Linus Pauling, benzene has a resonance hybrid, which is the reason why the benzene ring is very stable, and also directly leads to the aromaticity of the benzene ring.