O-perfluoroalkyl thiocarbamates: Synthesis and perfluoroalkyl effects on the barrier to NCS rotation

A series of new O-perfluoroalkyl thiocarbamates were synthesized by the reaction of isothiocyanates with perfluoroalkyl alcohols. Substituent effects on the barrier to rotation around the NCS bond in these thiocarbamates were investigated using variable temperature 1H NMR spectroscopy. The free energies of activation were in the range 14–17 kcal/mol and are attributed to the conformational S-cis and S-trans isomerization. The results obtained for different O-perfluoroalkyl thiocarbamates were discussed and compared with those of non-fluorinated analogs.