Experimental and theoretical studies of the vibrations and structure of 2,2,2-trifluoroethyl trifluoroacetate, CF 3CO 2CH 2CF 3

Abstract

The molecular structure of 2,2,2-trifluoroethyl trifluoroacetate, CF 3CO 2CH 2CF 3, has been determined in the gas-phase from electron-diffraction data supplemented by ab initio (MP2) and DFT calculations using basis sets up to 6-311++G(d,p). Both experimental and theoretical data indicate that, although both structures with anti, anti ( C s) and anti, gauche ( C 1) conformations exist by rotating about the O C(H 2) bond, the anti, anti structure is preferred. The difference in free energy was calculated to be 2.1 kJ mol −1 ( C s conformer lower in energy) and as the C 1 conformer has a double multiplicity relative to the C s conformer, the ratio of C 1– C s conformer was predicted to be 0.41: 0.59. This conformational preference was studied using the total energy scheme and the natural bond orbital partition scheme. Additionally, the total potential energy has been deconvoluted using six-fold decomposition in terms of a Fourier-type expansion. Infrared spectra of CF 3CO 2CH 2CF 3 have been obtained for the gaseous, liquid and solid phases and the Raman spectrum for the liquid phase. Harmonic vibrational frequencies and a scaled force field have been calculated, leading to a final root-mean-square deviation of 7.3 cm −1.