A conformational and vibrational study of CF₃COSCH₂CH₃

The molecular structure and conformational properties of S-ethyl trifluorothioacetate, CF₃COSCH₂CH₃, were determined in the gas phase by electron diffraction and vibrational spectroscopy (IR and Raman). The experimental investigations were supplemented by ab initio (Møller Plesset of second order) and density functional theory quantum chemical calculations at different levels of theory. Both experimental and theoretical methods reveal two structures with C_s (anti, anti) and C₁ (anti, gauche) symmetries, although there are disagreements about which is more stable. The electron diffraction intensities are best interpreted with a mixture of 51(3)% anti, anti and 49(3)% anti, gauche conformers. This conformational preference was studied using the total energy scheme and the natural bond orbital scheme. In addition, the infrared spectra of CF₃COSCH₂CH₃ are reported for the gas, liquid and solid phases as well as the Raman spectrum of the liquid. Using calculated frequencies as a guide, evidence for both C_s and C₁ structures is obtained in the IR spectra. Harmonic vibrational frequencies and scaled force fields have been calculated for both conformers.