Coplanarity in 2,6-Dimethylazobenzenes: a ¹³C N.M.R. Study

Abstract

A number of 3- and 4-X-2′,6′-dimethylazobenzenes and 4-X-2,6-dimethylazobenzenes have been prepared, and their ¹³C N.M.R . Spectra have been measured. Comparison of the effect of X on the ¹³C N.M.R . chemical shifts for C4′ with that for the corresponding azobenzenes has been used as a probe for exploring the influence of the two introduced ortho-methyl groups on the degree of coplanarity of the azobenzene system and the efficiency of transmission of electronic effects from one ring to the other. The results support previous studies that have suggested that the methyl groups have a substantial effect on the planarity of the system, but, surprisingly, suggest that such loss of planarity has relatively little effect on the efficiencies of transmission of both polar and resonance effects between the two rings.