CoachA carbocation rearrangement is the migration, within a carbocation, of a hydrogen atom or an alkyl group with its bonding pair to the neighbouring cationic carbon, giving a more stable carbocation (a 1,2-shift).
Examples
Example 25.4 (A methyl shift)
3,3-Dimethylbut-1-ene and hydrogen chloride give a secondary carbocation next to a quaternary carbon; a methyl group moves across with its pair, making a tertiary cation. The main product is 2-chloro-2,3-dimethylbutane, whose skeleton differs from that of the alkene; 3-chloro-2,2-dimethylbutane is minor.