Exchange contributions to the internal rotation barrier ofo-xylene

Abstract

The various contributions arising from a perturbation theory which includes overlap and intermolecular potential are examined for the interaction of two methyl groups in o-xylene. The barrier to internal rotation is dominated by exchange interactions. The ground and excited electronic state barriers are calculated and the potential surface is examined to show the non-validity of the independent oscillator model. Torsional frequencies are calculated and shown to agree reasonably well with the hot bands observed in the ultra-violet spectrum. The entropy and heat capacity at constant pressure have also been evaluated using calculated energy levels and are in reasonable agreement with the published values.