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Pinacol-Pinacolone Rearrangement

About Pinacol-Pinacolone Rearrangement

The acid catalysed rearrangement of vic diols (1, 2-diols) to ketones or aldehydes with elimination of water is known as pinacol or pinacol-pinacolone rearrangement. The name was given from the classical example of the conversion of pinacol to pinacolone.

Pinacol-Pinacolone Rearrangement

Reaction Mechanism of Pinacol-Pinacolone Rearrangement

The loss of water and migration of the alkyl group may be very rapid or simultaneous. Probably the migrating group does not become completely free before it is partially bonded.

(III) to the adjacent positively charged carbon, i.e., a type of intramolecular rearrangement is suggested.

Mechanism of Pinacol-Pinacolone Rearrangement

Evidence in favour of this are the migrating group retains its configuration, if chiral no cross-over products are obtained when a mixture of two nearly similar 1,2-diols is treated with acid.
Migratory aptitude: Migration order in general is H > aryl > alkyl . As the migrating group migrates with its electron pair, the more nucleophilic group might be expected to migrate. Thus, the order of migration amongst the aryl groups is p-anisyl > p-tolyl > phenyl > p-chlorophenyl, etc.

Pinacol-Pinacolone Rearrangement

Example of Pinacol-Pinacolone Rearrangement

 

Pinacol-Pinacolone Rearrangement

Example of Pinacol-Pinacolone Rearrangement

Related Reactions

List of Name Reaction of Organic Chemistry consist of detail Reaction Mechanism of all name reactions of Organic Chemistry.

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