Carbocation by using

In Chapter 17 we showed you that it is possible to run the NMR spectra of carbocations by using a polar but nonnucleophilic solvent such as liquid SO2 or SOC1F. Treating an alkyl halide RX with the powerful Lewis acid SbFs under these Conditions gives a solution of carbocation the carbocation reacts neither with solvent nor the SbF5X counterion because neither is nucleophilic. We know, for example, that the chemical shifts in both the l3C and NMR spectra of the f-butyl cation are very large, particularly the 13C shift at the positively charged centre. 

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