An N.M.R. study of the barrier to internal rotation, the molecular structure and the indirect spin-spin coupling constants ofo-xylene partially oriented in a nematic phase

Abstract

The N.M.R. spectrum of o-xylene partially oriented in a nematic phase has been measured, and the geometry of the proton skeleton and the indirect spin-spin coupling constants determined. The potential of internal rotation of the methyl groups has been studied, including coupling terms between the two rotors. No unique solution exists. However, choosing the most reasonable structure, and setting V ₆ = 0 and V ₃ = 2 kcal/mole, we obtain V_a = 0·29 ± 0·03 kcal/mole and V_g = 0·37 ± 0·08 kcal/mole where V ₆ is the normal six-fold potential, V ₃ is the normal three-fold potential, V_a is the barrier to the methyl groups rotating in the same direction and V_g is the barrier to the methyl groups rotating in opposite directions.