1,2-rearrangement

Chemical reaction involving the migration of a substituent from one atom to an adjacent atom

1,2-Rearrangement is a type of rearrangement reaction in which a substituent moves from one atom to an adjacent atom within a molecule. This process is a fundamental transformation in organic chemistry and can lead to significant changes in the structure and properties of the molecule.

Mechanism

In a 1,2-rearrangement, the migration of a substituent occurs between two adjacent atoms, typically involving a carbon atom. The rearrangement can proceed through a variety of mechanisms, including radical, cationic, and anionic pathways. The driving force for the rearrangement is often the formation of a more stable intermediate or product.

Radical Mechanism

In a radical mechanism, the rearrangement involves the movement of a substituent via a free radical intermediate. This type of rearrangement is often initiated by the homolytic cleavage of a bond, leading to the formation of radicals that can undergo migration.

Cationic Mechanism

Cationic 1,2-rearrangements involve the migration of a substituent in the presence of a carbocation intermediate. These rearrangements are common in reactions such as the Wagner-Meerwein rearrangement, where the migration leads to a more stable carbocation.

Anionic Mechanism

Anionic rearrangements involve the migration of a substituent in the presence of a negatively charged intermediate. These rearrangements are less common but can occur under specific conditions where an anion is stabilized by the surrounding molecular environment.

Examples

Wieland Radical Rearrangement

The Wieland radical rearrangement is a classic example of a radical 1,2-rearrangement. In this reaction, a radical species undergoes a 1,2-shift, resulting in the migration of a substituent to an adjacent position.

Aryl 1,2-Shift

An aryl 1,2-shift involves the migration of an aryl group from one position to an adjacent position within a molecule. This type of rearrangement can occur under specific conditions and is often facilitated by the presence of a suitable leaving group or catalyst.

Applications

1,2-Rearrangements are utilized in the synthesis of complex organic molecules. They are valuable tools in synthetic chemistry for constructing new carbon-carbon bonds and for the functionalization of molecules. These rearrangements are also important in the biosynthesis of natural products and in the development of pharmaceuticals.

Related pages

• Rearrangement reaction
• Wagner-Meerwein rearrangement
• Carbocation
• Free radical

Gallery

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  General scheme of a 1,2-rearrangement

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  Wieland radical rearrangement

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  Aryl 1,2-shift

1,2-rearrangement

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  1,2-rearrangement

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  Wieland Radical Rearrangement

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  Aryl 1,2-shift