Experimental and theoretical structure and vibrational analysis of ethyl trifluoroacetate, CF₃CO₂CH₂CH₃

The molecular structure and conformational properties of ethyl trifluoroacetate, CF₃CO₂CH₂CH₃, were determined in the gas phase by electron diffraction, and vibrational spectroscopy (IR and Raman). The experimental investigations were supplemented by ab initio (MP2) and DFT quantum chemical calculations at different levels of theory. Experimental and theoretical methods result in two structures with C_s (anti-anti) and C₁ (anti-gauche) symmetries, the former being slightly more stable than the latter. The electron-diffraction data are best fitted with a mixture of 56% anti-gauche and 44% anti-anti conformers. The conformational preference was also studied using the total energy scheme, and the natural bond orbital scheme. Also, the infrared spectra of CF₃CO₂CH₂CH₃ are reported for the gas, liquid and solid states, as is the Raman spectrum of the liquid. The comparison of experimental averaged IR spectra of C_s and C₁ conformers provides evidence for the predicted conformations in the IR spectra. Harmonic vibrational wavenumbers and scaled force fields have been calculated for both conformers.