Preparation and properties of trifluorothioacetic acid-5-(trifluoromethyl) ester, CFC(O)SCF

Trifluorothioacetic acid-S-(trifluoromethyl)ester, CFC(O) SCF, was prepared by reacting CFC(O)Cl and AgSCF at 50 °C. The compound was characterized by C-, F-NMR, UV, and vibrational spectroscopy as well as by gas electron diffraction (GED) and quantum chemical calculations (HF, MP2, and B3LYP methods 6-31G(d) and 6-311+G(2df) basis sets). GED and vibrational spectroscopy result in the presence of a single conformer with C symmetry and synperiplanar orientation of the S-CF bond relative to the C = O bond. This result is in agreement with quantum chemical calculations which predict the anti conformer to be higher in energy by about 4 kcal/mol. An assignment of the IR (gas) and Raman (liquid) spectra is proposed, and the GED analysis results in the following skeletal geometric parameters (r and ∠a values with 3σ uncertainties; these parameters are thermal averages and are not inconsistent with calculated equilibrium values): C = O = 1.202(6) Å, C-C = 1.525(10) Å, S-C(sp) = 1.774(3) Å, S-C(sp) = 1.824 (3) Å. O = C-C = 118.7(21)°, O = C-S = 127.1(15)°, C-S-C = 99.8 (13)°. © 2008 American Chemical Society.