New Description of the Substituent Effect on Electronic Spectra by Means of Substituent Constants. II. n-π and π-π Transitions

Abstract

In order to confirm and to extend the scope of the equation ^{1, 3}E^UV_ho→lu=aF+bR+c, presented by us in the foregoing paper, the polarographic half-wave reduction (E^red_1/2) and oxidation (E^oxd_1/2) potentials in nonaqueous media and the electronic spectra of 4-substituted azobenzenes have been analyzed. Although the equation was originally derived for π-π^* type HOMO→LUMO transitions with the same character in a series of substances, in this paper we have theoretically verified that the equation is also applicable to the n-π^* bands of conjugated systems. The singlet n-π^* and π-π^* bands of 4-substituted azobenzenes and the triplet n-π^* bands of 4, 4'-disubstituted benzophenones were employed to examine the above equation. The results were reasonable, and are discussed from the viewpoint of molecular orbital theory.