NEW DESCRIPTION OF THE SUBSTITUENT EFFECT ON ELECTRONIC-SPECTRA BY MEANS OF SUBSTITUENT CONSTANTS .7. ELECTRONIC-SPECTRA OF SUBSTITUTED BENZENES

The substituent effect on the first and second singlet pi-pi* bands of substituted benzenes is discussed on the basis of general equations. These equations were derived theoretically in order to describe the substituent effect on electronic spectra by means of substituent constants. The first band of substituted benzenes corresponding to the benzene 1L(b) band is well explained by the equation, but its application to the second band was not so good. This is due to the fact that the contribution from intramolecular charge-transfer configurations to the second band is quite dependent on substituents, so the character of the second band is not the same for all the substitutents. A theoretical study of the molecular orbital with regard to these results is reported, and the limit of application of our equation is discussed.