RESONANCE RAMAN STUDIES OF BENZENE-DERIVATIVES WITH STRONG CONJUGATION - NITRILE SUBSTITUTION

Raman spectra in resonance with the L(a) state of benzene derivatives exhibit activity in both the fundamental and two-quantum overtones of modes that are of e(2g) symmetry in benzene. The Raman spectra can be used to test proposals of Petruska that result in the conclusion that 1,2,3-trisubstituted benzenes should have L, transitions with very sma ll allowed transition moments. We find that nitrile substitution resul ts in absorption and resonance Raman spectra that show deviations from Petruska's rules. The 1,2,3-tricyano derivative exhibits Raman spectr a that demonstrate allowed transition character.