Two-dimensional vibrational potential energy surface for the ring bending and twisting of 1,3-oxathiolane. Evidence for the anomeric effect resulting from –O–CH2–S– linkages

Abstract

The far-infrared spectra of 1,3-oxathiolane and its 2,2-d2 isotopomer have been analyzed in terms of a two-dimensional vibrational potential energy surface expressed as a function of ring-bending and ring-twisting coordinates. The barrier to planarity was determined to be 2289±200 cm−1 while the barrier to pseudorotation, representing the energy difference between the lowest energy twisted form and the highest energy bent form, was found to be 570±20 cm−1. The barrier to planarity is about 500 cm−1 higher than that of cyclopentane, and this is attributed to the anomeric effect resulting from the –O–CH2–S– linkage which tends to twist the molecule out of the planar configuration.