RING CURRENT CONTRIBUTIONS TO VIBRATIONAL CIRCULAR-DICHROISM - ABINITIO CALCULATIONS FOR METHYL GLYCOLATE-D1 AND GLYCOLATE-D4

Vibrational rotational strengths are predicted for the hydrogenic stretching transitions of methyl glycolate-d1 (*CHD-(OH).COOCH3) and -d4 (*CHD(OH).COOCD3) using Stephens' a priori theory, implemented at the SCF level of approximation using the 6-31G* basis set. Five conformations are studied; four contain internally hydrogen-bonded rings, one does not. Predicted rotational strengths vary substantially with conformational structure but, for the *C-H and *C-D stretching modes, show no significant correlation with the existence of an internally hydrogen-bonded ring. For each isotopomer a detailed analysis of the rotational strengths of the *C-H and *C-D stretching transitions of two structures, with and without a hydrogen-bonded ring and differing in geometry only in the position of the OH H atom, shows that formation of the ring does not lead to significant enhancement in the magnetic dipole transition moment component perpendicular to the ring for these transitions. Our results are contrary to the expectations of the ring current hypothesis of Nafie and co-workers and lead to the conclusion that this hypothesis does not provide a sound foundation for the interpretation of VCD spectra.