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Rearrangement reaction

 

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Rearrangement reaction



 
 
A rearrangement reaction is a broad class of organic reaction
Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and organic redox reaction....
s where the carbon skeleton of a molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 is rearranged to give a structural isomer of the original molecule . Often a substituent
Substituent

In organic chemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon. The suffix -yl is used when naming organic compounds that contain 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:

Intermolecular rearrangements also take place.

A rearrangement is not well represented by simple and discrete electron transfers (represented by curly arrows in organic chemistry texts).






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A rearrangement reaction is a broad class of organic reaction
Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and organic redox reaction....
s where the carbon skeleton of a molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 is rearranged to give a structural isomer of the original molecule . Often a substituent
Substituent

In organic chemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon. The suffix -yl is used when naming organic compounds that contain 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:

Intermolecular rearrangements also take place.

A rearrangement is not well represented by simple and discrete electron transfers (represented by curly arrows in organic chemistry texts). The actual mechanism of alkyl groups moving, as in Wagner-Meerwein rearrangement
Wagner-Meerwein rearrangement

A Wagner-Meerwein rearrangement is a class of carbocation 1,2-rearrangement rearrangement reactions in which a hydrogen, alkyl or aryl group migrates from one carbon to a neighboring carbon....
, 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 curly arrows for a sequence of discrete electron transfers that give the same result as a rearrangement reaction, although these are not necessarily realistic.

Some key rearrangement reactions:
  • 1,2-rearrangement
    1,2-rearrangement

    A 1,2-rearrangement or 1,2-migration or 1,2-shift or Frank C. Whitmore 1,2-shift is an organic reaction where a substituent moves from one atom to another atom in a chemical compound....
    s
  • pericyclic reactions
  • olefin metathesis
    Olefin metathesis

    Olefin metathesis or transalkylidenation is an organic reaction that entails redistribution of alkylene fragments by the scission of carbon - carbon chemical bond in olefins....


Examples are the Wagner-Meerwein rearrangement
Wagner-Meerwein rearrangement

A Wagner-Meerwein rearrangement is a class of carbocation 1,2-rearrangement rearrangement reactions in which a hydrogen, alkyl or aryl group migrates from one carbon to a neighboring carbon....
:

the Beckmann rearrangement
Beckmann rearrangement

The Beckmann rearrangement, named after the German chemist Ernst Otto Beckmann , is an acid catalysis rearrangement reaction of an oxime to an amide....
:

and the Claisen rearrangement
Claisen rearrangement

The Claisen rearrangement is a powerful carbon-carbon chemical bond-forming chemical reaction discovered by Rainer Ludwig Claisen. The heating of an allyl vinyl ether will initiate a Sigmatropic reaction to give a ?,d-unsaturated carbonyl....
:

Claisen Rearrangement Scheme