Ab initio study of the conformational equilibrium of trimethylene cyclic sulfite

Ab initio calculations, in the frame of MO theory, were carried out on both most stable (chair) conformers of trimethylene cyclic sulfite. Optimized g eometries derived at the HF/6-31G* level reveal that both conformers posses s a rigid chair conformation with the S=O group located either axially (con former I) or equatorially (conformer II). Energy calculations at the MP2/6- 311++G**//HF/6-31G* level indicates that conformer I is ca 4.6 kcal. mol(-1 ) more stable than II. The I = II interconversion was studied in the gas ph ase at different temperatures and in solutions of low- and high-polarity so lvents. The calculations reveal that in the gas phase and in solutions of l ow-polarity solvents the conversion of I into II does not occur. In medium- high-polarity solvents, such as acetonitrile and dimethyl sulfoxide, II is present at ca 12%. Copyright (C) 2000 John Wiley & Sons, Ltd.