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

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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 Va = 0·29 ± 0·03 kcal/mole and Vg = 0·37 ± 0·08 kcal/mole where V 6 is the normal six-fold potential, V 3 is the normal three-fold potential, Va is the barrier to the methyl groups rotating in the same direction and Vg is the barrier to the methyl groups rotating in opposite directions.