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

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