Detection of Carbocations

The study of carbocations illustrates many of the ways in which reactive intermediates are studied. In particular, both H and NMR have been among the primary instrumental methods applied to the structure and properties of carbocations. A pioneer in the field was Olah, who found that under appropriate conditions organic precursors dissolved in superacid media (such as S02ClF-SbF5 solution, often at low temperature) gave solutions with spectra consistent with the presence of relatively long-lived carbocations. 

Intuitively, we might expect electron-donating alkyl substituents on a carbenium center to increase the local electron density and thus the shielding at that site. 

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