Mutual correlation between nonaqueous oxidation-reduction potentials and electronic spectra, and its extension to describe the substituent effect on electronic spectra by means of substituent constants.

Abstract

In order to confirm and to extend the scope of the equation (Eoxd1/2-Ered1/2)=k11, 3 EUVho-lu+k2, presented previously by us, the polarographic half-wave reduction (Ered1/2) and oxidation (Eoxd1/2) potentials in nonaqueous media and the electronic spectra of 4, 4'-disubstituted stilbenes have been measured and analyzed by means of the equation with reasonable results. The substituent effect on Eoxd1/2 and Ered1/2 values has been well described by using the Hammett-type substituent constants. This result has been combined with the above equation, and thus a general equation describing the substituent effect on electronic spectra in terms of substituent constants has been derived as EUVho-lu=aF+bR+c, F and R being Swain and Lupton's substituent constants. This equation has been experimentally examined using the strong longest-wavelength π-π* bands of 4, 4'-disubstituted stibenes and azoxybenzenes. The results were quite reasonable. Finally, the description of the substituent effect on electronic spectra in terms of substituent constants is discussed on the basis of molecular orbital theory.