AbstractA simple correlation between the MO bond orders and the resonance structures of a π system is proposed. Para conjugation is a resonance structure with parallel arrangement of alternating attractive and repulsive bonds. The results in C5H5−, C6H6and C77+clearly show that the para conjugation is very important comparing with the ordinary ring conjugation. The aromatic substitution reactions strongly demomstrates the effect of para conjugation in benzene, naphthalene and anthran