8.1 Types of Rearrangements

Rearrangements are divided into intramolecular and intermolecular processes. In intramolecular process, the group that migrates is not completely detached from the system in which rearrangement is taking place. In contrast, in intermolecular process, the migrating group is first detached and later re-attached at another site.

8.2 Rearrangement to Electron Deficient Carbon

These reactions are classified according to the nature of group that migrates.

8.2.1 Carbon Migration

8.2.1.1 Wagner-Meerwein Rearrangement

It is one of the simplest systems where an alkyl group migrates, with its bonding pair, to an electron-deficient carbon atom.

Mechanism

The driving force for the rearrangement resides in the greater stability of a tertiary carbocation compared to that of primary carbocation.

The classical and non-classical carbocation controversy concerned the Wagner-Meerwein rearrangement of norbornyl systems: