Rearrangement of Carbocations

Alkyl groups have a slight electron releasing effect. Hence a carbocation is more stable when the positive centre is more substituted by alkyl groups. I.e. in terms of stability, tertiary > secondary > primary. If a carbocation is formed in such a way that an alkyl shift can improve the stability of said carbocation, this rearrangement may occur. Hence a mixture of products may be obtained from the reaction. This is unfavourable if one wishes to prepare a specific compound.