Experimental and theoretical studies of the vibrations and structure of 2,2,2-trifluoroethyl trifluoroacetate, CF₃CO₂CH₂CF₃

The molecular structure of 2,2,2-trifluoroethyl trifluoroacetate, CF₃CO₂CH₂CF₃, 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 (C₁) conformations exist by rotating about the O-C(H₂) 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 C₁ conformer has a double multiplicity relative to the C_s conformer, the ratio of C₁: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 CF₃CO₂CH₂CF₃ 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.