Rearrangement reaction

A rearrangement reaction are organic reactions where the carbon skeleton of a molecule is rearranged. The result is a structural isomer of the original molecule.[1] Often a substituent moves from one atom to another atom in the same molecule. In the example below, the substituent R moves from carbon atom 1 to carbon atom 2:

General scheme rearrangement

Intermolecular rearrangements also take place.

Sometimes chemists draw diagrams with arrows that show how electrons are transferred between bonds during a rearrangement reaction. Many organic chemistry text books have such diagrams. But they do not tell the full story of the reaction mechanism. The actual mechanism of a rearrangement with an alkyl group moving is for the group to slide smoothly along a bond, not ionic bond-breaking and forming. One example of this is the Wagner-Meerwein rearrangement:

In pericyclic reactions, the orbital interactions are important. The reactions can not be explained by a series of simple discrete electron transfers. But, the curved arrows showing a sequence of discrete electron transfers can give the same result as a rearrangement reaction. Yet, the diagrams are not necessarily realistic. In allylic rearrangement, the reaction is ionic.

Three important rearrangement reactions are 1,2-rearrangements, pericyclic reactions and olefin metathesis.