Valence bond descriptions of benzene and cyclobutadiene and their counterparts with localized bonds

Geometry optimizations have been performed for benzene and cyclobutadiene and for the corresponding moieties with nonresonating double bonds, viz. 1,3,5‐cyclohexatriene and 1,3‐cyclobutadiene. The calculations were done using the valence bond self‐consistent field method including orbital optimization. Both strictly local and delocalized p‐like orbitals were used for the π system, which influences the strengths of the π bonds. The calculations result in geometries and resonance and stabilization energies for benzene and cyclobutadiene, which are compared with theoretical models of aromaticity. The importance of resonance is discussed.