Polarization effects in small rings containing sulfur. A theoretical study of the structure of thiete

Abstract

The structure of thiete has been optimized at several levels of accuracy within the framework of ab-initio SCF calculations. The results obtained show that thiete is a nonpuckered four-membered ring, which is in agreement with the experimental evidence. The STO-3G and STO-3G* basis sets are neither adequate nor well balanced enough to describe this kind of molecule. Polarization functions must be added to reasonably sized sp bases in order to avoid non-physical results and incorrect descriptions of the polarity of the molecule. As for other non-cyclic systems containing second-row atoms, the 3-21G and 4-31G split-valence basis sets lead to remarkably similar geometries, however an adequate description of the geometry and polarity of thiete requires the inclusion of polarization functions in the basis set. Polarization of the valence-shell of sulfur is crucial and more important than at other regions of the ring. This can be attained by supplementing a reasonably sized sp basis set with d functions or BFs. Similarly, as has been found for other small cycles, ring functions (RFs) constitute a good and cheap alternative to the usual BFs.