Rearrangement reaction

In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule.^[1] Often a substituent moves from one atom to another atom in the same molecule, hence these reactions are usually intramolecular. In the example below, the substituent R moves from carbon atom 1 to carbon atom 2:

${\displaystyle {-}{\underset {| \atop \displaystyle \color {Blue}{\ce {R}}}{{\ce {C}}}}{\ce {-C-C{-}-> {-C-}}}{\underset {| \atop \displaystyle \color {Blue}{\ce {R}}}{{\ce {C}}}}{\ce {-C}}{-}}$

Intermolecular rearrangements also take place.

A rearrangement is not well represented by simple and discrete electron transfers (represented by curved arrows in organic chemistry texts). The actual mechanism of alkyl groups moving, as in Wagner–Meerwein rearrangement, probably involves transfer of the moving alkyl group fluidly along a bond, not ionic bond-breaking and forming. In pericyclic reactions, explanation by orbital interactions give a better picture than simple discrete electron transfers. It is, nevertheless, possible to draw the curved arrows for a sequence of discrete electron transfers that give the same result as a rearrangement reaction, although these are not necessarily realistic. In allylic rearrangement, the reaction is indeed ionic.

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