Conformational properties of F2SNCF2NSF2 and F2SNCF2NS(O)F2: Vibrational spectra and quantum chemical calculations

The structural and conformational properties of F2SNCF2NSF2 and F2SNCF2NS(O)F2 were studied by vibrational spectroscopy (IR(gas) and Raman(liquid)) and by quantum chemical calculations, using B3LYP and MP2 methods with small and large basis sets. Since the SF2 and S(O)F2 groups can adopt syn (s) or anti (a) position (syn/anti of the FSF bisector with respect to the adjacent NC bond) and the orientation around the two NC bonds can be trans (t) or gauche (g), a large number of possible conformers is expected. In the case of F2SNCF2NSF2 calculations with large basis sets predict the presence of a single conformer with both SF2 groups in syn position and gauche orientation around both NC bonds (s–g–g–s conformer). This is confirmed by the vibrational spectra. For F2SNCF2NS(O)F2 analysis of the vibrational spectra in combination with the quantum chemical calculations suggests the predominance of the s–g–t–s conformer, i.e. syn position of SF2 and S(O)F2 groups, gauche orientation around one NC bond and trans orientation around the other NC bond, and the presence of a smaller amounts of the s–t–g–s and s–g–g–s conformers.