Additivity of substituent effects on the proton–proton coupling constants in substituted benzenes. Investigation of some trisubstituted benzenes

Abstract

An additivity scheme based on the changes in ortho, meta, and para proton coupling constants of benzene induced by a single substituent is applied to a number of trisubstituted benzenes. Ortho coupling constants are well reproduced (root mean square deviations = 0.05 c.p.s.) by the scheme but for meta and para couplings saturation effects are indicated. For the latter two couplings there are two substituents ortho to one of the protons involved. Measurements indicate that a temperature range of 100 °C has a negligible effect on the couplings but that polar solvents are to be avoided in obtaining data for the testing of additivity schemes.