Preparation, C-13 NMR and IGLO/DFT studies of trifluoromethyl substituted allyl cations

alpha-Trifluoromethyl substituted allyl cations 3 and 4 have been prepared by ionizing their corresponding alcohols with SbF5 in SO2ClF at low temperatures. The barriers to rotation around the C1-C2 bond of the both cations were determined to be about 9 kcal/mol. The unusually low barriers as compared with their methyl analogues are rationalized by the unsymmetrical nature of the cations. CF3-substituted cyclohexenyl cations 8 and 10 were also prepared and characterized by C-13 NMR spectroscopy. Density functional theory (DFT) calculations were performed to investigate geometries and charge densities of tifluoromethyl substituted allyl cations. C-13 NMR chemical shifts of the cations were also calculated by IGLO method and compared with the experimental results.