Structures and Conformations of ((Trifluoroacetyl)imido)(trifluoromethyl)sulfur Fluoride, CF3C(O)NS(F)CF3

The molecular structure and conformational properties of ((trifluoroacetyl)imido)(trifluoromethyl)sulfur fluoride, CF 3 C(O)N=S(F)CF 3 , were determined by gas electron diffraction (GED) and vibrational spectroscopy (IR (gas) and Raman (liquid)). Furthermore, quantum chemical calculations (HF, MP2, and B3LYP with 6-31G* basis sets) were performed. The vibrational spectra were assigned by comparison with related molecules and calculated (HF and B3LYP) frequencies and intensities. According to the GED analysis the main conformer (90(6)%) possesses an anti-syn structure with anti orientation of the N-C bond relative to the F-S-CF 3 bisector and syn orientation of the C=O bond relative to the N=S bond. The second conformer (10(6)%) possesses a syn-syn structure. The experimental Gibbs free energy difference (ΔG° = 1.3(4) kcal/mol) is reproduced correctly by the two quantum chemical methods (1.35 kcal/mol from MP2 and 1.04 kcal/mol from B3LYP). The conformational properties of this compound are in contrast to those of imidosulfurous difluorides, RNSF 2 , and dichlorides, RN=SCl 2 , for which only syn structures around the N=S double bond were observed.