30: Cationic Rearrangements

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In the first half of the nineteenth century it was generally believed that reactions of organic compounds proceeded with minimal structural change. This tenet simplified the elucidation of the numerous substitution, addition and elimination reactions that characterized the behavior of common functional groups. However, subsequent discoveries showed that nature was not always so obliging, leaving chemists and chemistry students to grapple with the possibility of deep seated structural change occurring during certain reactions. A large number of these structural rearrangements are triggered by intermediates incorporating positively charged or electron deficient atoms, which in the case of carbon are carbocations. Two such examples, already noted, are the addition of HCl to 3,3-dimethyl-1-butene and forced hydrolysis of neopentyl bromide. This chapter will describe and discuss other cases of this intriguing group of transformations.