Conformational Analysis of Trifluoroacetyl Triflate, CF₃C(O)OSO₂CF₃: Experimental Vibrational and DFT Investigation

Abstract

The conformations of trifluoroacetyl triflate, CF3C(O)OSO2CF3, were investigated through vibrational experimental methods (gas-phase FTIR, liquid-phase Raman, and Ar-matrix FTIR spectroscopy) and Density Functional Theory (DFT) calculations. A potential energy surface was computed using the B3P86 /6-31+g(d) approximation as a function of the dihedral angles τ1 = CCOS and τ2 = COSC. The surface reveals three minima, which were further optimized using the B3LYP method with various basis sets (6-31++G(d), 6-311++G(d), tzvp and cc-pvtz). The global minimum corresponds to a syn-anti conformer (the CO double bound syn with respect the O−S single bond and the C−O single bond anti with respect to de S−C single bond). The other two minima represent enantiomeric syn-gauche forms. The Ar-matrix FTIR spectrum exhibited clear evidence of the presence of two conformers. Furthermore, the randomization process observed following broad-band UV-visible irradiation facilitated the identification of the IR absorption of each conformer. Based on the Ar-matrix FTIR experiments, the vapour phase of trifluoroacetyl triflate at room temperatures was composed of approximately 60-70% of the syn-anti conformer and 30-40% of the syn-gauche form.