Spectroscopic and structural studies on phenyl and pentafluorophenyl trifluorothioacetate, and pentafluorophenyl...

Phenyl and pentafluorophenyl trifluorothioacetate, CF₃C(O)SC₆H₅ and CF₃C(O)SC₆F₅, were prepared by condensation of CF₃C(O)Cl and the corresponding mercaptan RSH under vacuum conditions. The compounds were isolated and properly characterized by using infrared spectroscopy, UV-Vis, multinuclear NMR spectroscopy techniques and by mass spectrometry. The crystal structures have been determined for both CF₃C(O)SC₆H₅ and according to the best of our knowledge the not yet reported in the literature CF₃C(O)SC₆F₅ species. The conformational preferences of the three title species were also determined by means of FTIR spectroscopy. In the case of CF₃C(O)OC₆F₅, the FTIR spectrum was also measured in an Ar-matrix and a subsequent photochemical study was performed. The main stable photoproduct found, beside CO, was the ether C₆F₅OCF₃. Quantum-chemical calculations were used to determine the conformational preferences and complement the experimental structure parameters as well as to interpret the UV-Vis spectra determined for the three species under study. As a result of all these experimental determinations complemented with computational calculations, it can be affirmed that the title compounds present a single syn conformation in the analyzed phases (syn with respect to the CO double bond and the opposite C-chalcogen single bond). This finding reconfirms the syn conformational transferability found so far for both thioesters and esters, a result that is closely related to the properties of these families in biological processes.