Benzoannelated quinone methides

Abstract

On the basis of detailed study of UV, IR, 13C NMR and E1/2 data of quinone methides V-VII three dominant factors influencing the behaviour of benzoannelated compounds must be considered: 1) electronic effects of both the exocyclic carbon substituents and the fused rings, 2) the extent to which the substituents are displaced out of the plane of the exocyclic double bond through steric interference between the side-chain substituents and peri-hydrogens and 3) the extent of the angular distorsion of the quinone-like rings. The ground state charge separation (~0.2e) in nonannelated derivatives was found to be strongly minimized by annelation of two benzene units to the parent systems. Near parallelism with this phenomenon was also observed in both the carbonyl vibration frequency and 13C NMR data.