Rearrangement

from Wikipedia, the free encyclopedia

A rearrangement or rearrangement reaction is a type of reaction in organic chemistry . Such a chemical reaction leads to a migration of individual atoms or groups of atoms within a molecule ( intramolecular ). This structural reorganization of the original molecule creates a new chemical compound . Here is a carbon-carbon or carbon- hetero atom - bond cleavage and recharge of groundwater instead. This includes both single-stage migrations and multi-stage reactions in the course of which such a migration occurs.

Basics

1,2 rearrangement (formal)

If an atom or a functional group moves from one atom to the next neighboring atom, this is called a [1,2] rearrangement. Accordingly, rearrangements to neighbors further away from the original atom are called [1,3] -, [1,4] - etc. rearrangements. One speaks of sigmatropic processes (migration of a σ bond).

The splitting off and migration of the functional group or the atom can be polar ( nucleophilic , electrophilic ) or non-polar ( radical , pericyclic ). In nucleophilic, including anionotropic , rearrangements, the remainder migrates with an electron pair and in electrophilic or cationotropic rearrangements without an electron pair, while in radical rearrangements the group migrates as a radical . In the case of pericyclic rearrangements, however, the remainder migrates along a π system with the formation of a cyclic transition state . These are known as sigmatropic rearrangements .

The residue remaining after a group has migrated, such as a carbenium ion in the case of nucleophilic rearrangements , must be stabilized by suitable reactions. In the case of a carbenium ion, this can be done by splitting off a proton, by nucleophilic substitution or by forming a double bond.

Examples of rearrangements in organic chemistry

Polar rearrangements

Most polar rearrangements are [1,2] rearrangements. Electron sextet species such as carbenium ions , carbenes or nitrenes can, but do not have to, be passed through.

Anionotropic rearrangements

In the case of anionotropic rearrangements, the rearrangement group migrates with the pair of binding electrons out of the sigma bond, which is separated. The group thus migrates formally as an anion.

[1,2] rearrangements in carbenium ions
[1,2] rearrangements of carbenes and carbenoids
[1,2] rearrangements without sextet intermediates

Cationotropic rearrangements

Non-polar rearrangements

Radical rearrangements

Pericyclic rearrangements (sigmatropic rearrangements)

  • [1,3] sigmatropic rearrangement
  • [1,5] sigmatropic rearrangement
  • [1,7] sigmatropic rearrangement
  • Sommelet-Hauser rearrangement, [2,3] sigmatropic rearrangement
  • Claisen rearrangement , [3,3] sigmatropic rearrangement
  • Cope rearrangement , [3,3] sigmatropic rearrangement
  • Benzidine rearrangement , [5,5] sigmatropic rearrangement,
in which benzidine is formed from hydrazobenzene under the action of acids . In the course of gross similar acid-catalyzed reactions N -substituted aryl amines (examples: N -Alkylanilin , N -Nitroso- N -alkylanilin, N -Chloranilin , phenylhydroxylamine , Phenylsulfaminsäure and diazoaminobenzene ) are mechanistically no real surroundings , because the migration of the substituent intermolecularly and not intramolecularly carried .

Prototropic isomerizations in unsaturated systems

In the case of unsaturated compounds, isomerizations can occur, which consist in the displacement of a double bond and a hydrogen atom. Examples of such isomerizations are

See also

literature

Individual evidence

  1. ^ I. Fleming, Frontier orbitals and organic chemical reactions, ISBN 3-527-25792-6 .
  2. Eberhard Breitmaier, Günther Jung: Organische Chemie, 7th edition, Thieme Verlag, 2012, p. 446, ISBN 978-3-13-541507-9 .
  3. a b Siegfried Hauptmann : Reaction and Mechanism in Organic Chemistry , BG Teubner, Stuttgart, 1991, pp. 145-146, ISBN 3-519-03515-4 .
  4. ^ Siegfried Hauptmann : Reaction and Mechanism in Organic Chemistry , BG Teubner, Stuttgart, 1991, pp. 146-148, ISBN 3-519-03515-4 .
  5. ^ Ivan Ernest: Binding, Structure and Reaction Mechanisms in Organic Chemistry , Springer-Verlag, 1972, pp. 259–261, ISBN 3-211-81060-9 .