chemical bonding (1.5 bond)

I think you are mentioning bond order.
in fact the bond order of benzene is 1.5, which means each carbon is connected to another 1.5 carbon.

this is conjugation, or resonance effect. the single/double/triple bond are covalent bond, but those 1.5 bond is not necessary covalent bond.

2008-09-05 16:09:40 補充：
0.5 bond means the bond electron density is not the same as the 1.0 bond electron density