On the equivalence of V6 to torsional flexing for molecules with threefold barriers to internal rotation

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Abstract
A comparison is made of the approaches of Lees and Baker and of Ewig and Harris to the Hamiltonian for internal rotation, both of which showed that the effects of a V6 term in a threefold torsional potential are identical to those of torsional flexing, i.e., to the distortion of molecular geometry due to torsion. The two approaches are proved to give identical results in the first order of perturbation. Earlier contrasting arguments that spectra could be explained by a V6 term but not by torsional flexing are examined and found to contain an incorrect averaging procedure in the perturbation treatment. Values of the torsional flexing term equivalent to published values of V6 are obtained to first order and are discussed. Although experimental information is not yet sufficiently precise or extensive to permit quantitative conclusions, it appears that torsional flexing could account for a significant part of the reported V6 in some cases.
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