CONFORMATIONAL PROPERTIES AND GAS-PHASE STRUCTURE OF (FLUOROCARBONYL)SULFENYL CHLORIDE, FC(O)SCI - ELECTRON-DIFFRACTION, VIBRATIONAL ANALYSIS, AND ABINITIO CALCULATIONS

The gas-phase structure and conformational composition of FC(O)SCI were determined by electron diffraction. The following geometric parameters (r(a) distances and angle-alpha angles with 3-sigma uncertainties) were derived for the trans conformer: C = O = 1.179(4) angstrom, C-F = 1.342(4) angstrom, S-C = 1.756(5) angstrom, S-Cl = 1.996(3) angstrom, C-S-Cl = 100.3(5)-degrees, S-C = O = 130.9(5)-degrees, S-C-F = 105.3(3)-degrees. The free-energy differences DELTA-G-degrees = G-degrees-(cis) - G-degrees-(trans) from the electron diffraction experiment (DELTA-G-degrees(ED) = 1.2(3) kcal/mol) and from matrix IR spectra (DELTA-G-degrees-(IR) = 1.4(1) kcal/mol) are equal within their estimated error limits. Ab initio calculations at various levels of theory (HF, MP2, and MP4) reproduce the experiment very well (DELTA-E = 1.25-1.60 kcal/mol). Additional calculations for thioformic acid and various fluorine- and/or chlorine-substituted derivatives reveal a strong substituent effect on the conformational properties.