Structures and Conformations of (Trifluoromethyl)thioacetic Acid, CF3C(O)SH, and Derivatives CF3C(O)SCH3 and CF3C(O)SCl

Abstract

The geometric structures and conformations of (trifluoromethyl)thioacetic acid, CF3C(O)SH, methyl trifluorothiolacetate, CF3C(O)SCH3, and trifluorothiolacetate chloride, CF3C(O)SCl, were determined by gas electron diffraction and theoretical calculations (ab initio and density functional methods). In the cases of CF3C(O)SCH3 and CF3C(O)SCl, the experimental scattering intensities are consistent only with the existence of a planar syn conformer (SCH3/SCl single bonds syn with respect to the CO double bond) in the gas phase. The theoretically predicted energy differences ΔE between anti and syn forms are 4.2 kcal mol-1 (HF/3-21G* and HF/6-31G*) for CF3C(O)SCH3 and 3.2 (HF/3-21G*) or 5.6 kcal mol-1 (HF/6-31G*) for CF3C(O)SCl. The conformational properties of CF3C(O)SH could not be determined unambiguously in the experiment. On the basis of the theoretical results (ΔE = 0.9−2.2 kcal mol-1), only a syn conformer was considered in the experimental structure analysis.