[phymatter]

are there some restrictions on the structure for carbocation rearrangement??

[Scatter]

Well, I don't know exactly what you mean when you say "restrictions" but there will never be a rearrangement that leaves the carbocation on a primary carbon.

From my understanding of it, rearrangements of a hydrogen or alkyl substituent happen to put the carbocation in a more stable position in the molecule, such as a teritiary or benzylic position.

[srihari]

please make the question more specific .