Interconversion Pathways of Chalcogen Rings. AnAb InitioMO Study of Model Reactions Involving Hypervalent Sulfur and Selenium Hydrides

Abstract

Chalcogen ring molecules are known to undergo facile interconversion reactions in organic solvents and in the melts, e.g. polymerization of liquid sulfur or the formation of Se6 and Se7 upon dissolving Se8 in CS2. These interconversion reactions have been suggested to proceed via the homolytic cleavage of the chalcogen-chalcogen bonds or through the formation of hypervalent intermediates. The experimental evidence on the actual mechanism, however, is rather sparse. The energetics of the various suggested interconversion pathways have been studied by ab initio MO techniques using suitable model reactions involving sulfur and selenium hydrides. Full geometry optimization has been performed for hypervalent chalcogen hydrides H2EE and H2E(EH)2 as well as for the radicals HE · and HEE · (E = S or Se in the case of each chalcogen atom) utilizing the MIDI-4∗ basis sets. The energy changes in their formation from appropriate unbranched chalcogen hydrides HEnH(n = 1,2 or 4) and HEnE′mH (m,n = 0–4; n + m = 2,4; E,E...