Molecular Structures and Conformations of Some Thioperoxides RS-OR': Experiment and Theory

摘要

All peroxides RO-OR' and disulfanes RS-SR', whose gas phase structures are known, possess gauche structures and most of them possess dihedral angles between 80° and 120°. Thioperoxides of the type RS-OR' are much less stable than peroxides and disulfanes and very little is known about their structural properties. Sulfenic acid, HSOH, dimethoxysulfane, CH_3OSOCH_3 and dimethoxydisulfane, CH_3OSSOCH_3, possess gauche structures with dihedral angles between 75° and 90°. A combination of vibrational spectroscopy, gas electron diffraction and quantum chemical calculations results for trifluoromethanesulfenyl acetate, CF_3S-OC(O)CH_3, and for trifluoromethanesulfenyl trifluoroacetate, CF_3S-OC(O)CF_3, in a mixture of two conformers with the prevailing component possessing gauche structure. The minor form (18(5)% and 11(5)%, respectively) possesses an unexpected trans structure around the S-O bond. The C=O bond of the acetyl group is oriented syn with respect to the S-O bond in both conformers. A similar experimental and theoretical study of S-(fluoroformyl)O-(trifluoroacetyl)thioperoxide, FC(O)S-OC(O)CF_3, results also in a mixture of two conformers. In this thioperoxide, however, both conformers possess gauche structure around the S-O bond and differ only by the orientation of the FC(O) group (C=O bond syn or anti with respect to the S-O bond).