Gas phase structure of methyl trifluoromethanesulfonate, CH3OSO2CF3, and conformational properties of covalent sulfonates

The molecular structure of methyl trifluoromethanesulfonate (CH3OSO2CF3, me thyl triflate) was investigated by gas electron diffraction (GED) and quant umchemical calculations (HF/3-21G* and B3LYP/6-31G*). The GED analysis reve aled a gauche conformation (methyl group gauche with respect to CF3 group) with a dihedral angle phi(C-O-S-C) 89(7)degrees. This value is reproduced c orrectly by the calculations. Some calculated bond lengths and bond angles, however, differ from experimental values by up to +/-0.07 Angstrom and +/- 6 degrees. Additional B3LYP/6-31G* calculations have been performed for som e covalent sulfonates. The potential functions for internal rotation around the S-O single bond in FOSO2F and ClOSO2F possess minima for gauche and tr ans orientation of the O-X (X = F or Cl) bond. The trans minima are 1.6 and 1.3 kcal mol(-1) higher in energy. The potential functions for triflic aci d, HOSO2CF3, for CH3OSO2Cl and CH3OSO2F possess minima only for gauche stru ctures and maxima for trans orientation. These results are in partial contr ast to previous experimental studies.