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Give the migratory order of pinacol pinacolone reaction

Give the migratory order of pinacol pinacolone reaction

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1 Answers

Bhavya
askIITians Faculty 1281 Points
8 years ago
Migratory aptitude, i.e.hydride>Phenyl> tertiary carbocation > secondary carbocation > methyl cation .

REASON:-

In the pinacol rearrangement, a 1,2-diol is treated with acid and rearranges to a carbonyl compound.
In this methyl migration can 1) help stabilize the developing carbocation center and 2) once fully migrated, produces a resonance stabilized hydroxyl-carbocation.
If one or more of the methyl groups is replaced with some other substituent (for example, alkyl, hydrogen, aryl), then our reaction possibilities become more complex; which hydroxyl group will protonate, which group will migrate? Generally, both hydroxyls will protonate and lead to separate products. In terms of which group will migrate, the only thing agreed upon is that a tertiary carbon will migrate in preference to a secondary carbon which will migrate in preference to a primary carbon.Clearly, the ability of the migrating group to stabilize positive charge plays a role.

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