Vibrational properties of some elusive members of the RNSO family: CF3NSO and SF5NSO

► A single syn conformer was found for SF5NSO and CF3NSO in the fluid phases. ► Orbital interactions explain the preference of a sterically unfavourable conformation. ► The numbers of features observed in the vibrational spectra confirms the presence of only one form. The vibrational spectra of N-(trifluoromethyl)sulfinylamine, CF3NSO and N-(pentafluorsulfanyl)sulfinylamine, SF5NSO have been recorded and assigned. According to quantum chemical calculations (B3LYP and MP2 with 6-31G(d) and 6-311+G(df) basis sets) the sterically unfavorable syn (Z-) conformers are 2.6–4.1kcal/mol (CF3NSO) and 3.1–4.6kcal/mol (SF5NSO) lower in free energy than the anti conformers. Such ΔG° values determine an equilibrium of 98.8% (syn) and 1.2% (anti) for CF3NSO, and ≈99% (syn) and