A 1,2-rearrangement or 1,2-migration or 1,2-shift or Whitmore 1,2-shift[1] is an organic reaction where a substituent moves from one atom to another atom in a chemical compound. In a 1,2 shift the movement involves two adjacent atoms but moves over larger distances are possible. In the example below the substituent R moves from carbon atom C2 to C3.
The rearrangement is intramolecular and the starting compound and reaction product are structural isomers. The 1,2-rearrangement belongs to a broad class of chemical reactions called rearrangement reactions.
A rearrangement involving a hydrogen atom is called a 1,2-hydride shift. If the substituent being rearranged is an alkyl group, it is named according to the alkyl group's anion: i.e. 1,2-methanide shift, 1,2-ethanide shift, etc.
- ^ Whitmore, Frank C. (1932). "The common basis of molecular rearrangements". Journal of the American Chemical Society. 54 (8): 3274–3283. doi:10.1021/ja01347a037.