Substituted Benzene Spectra

Abstract

The low‐lying π‐electron excited states of substituted benzenes are examined from a semiempirical point of view, by using molecular orbital theory together with first‐order configuration interaction as a basis. Different semiempirical parameters are introduced for the perturbations by a substituent upon states of different symmetry. Substituents exerting conjugative, inductive, and mixed effects are considered. Comparisons with experiment show that the experimentally observed facts concerning the effect of substitution upon the energy and intensity of these transitions are well accounted for by the theory. The relationship of the present treatment to that of the perimeter model introduced by Moffitt is discussed. The present model breaks down for very ``strong'' substituents when a higher‐order configuration interaction treatment becomes essential.