Spectroscopic and structural studies on phenyl and pentafluorophenyl trifluorothioacetate, and pentafluorophenyl trifluoroacetate, CF3C(O)SC6H5, CF3C(O)SC6F5 and CF3C(O)OC6F5

Abstract

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 CO 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.