Advanced Topic 875 of 1102 Organic Chemistry
Pinacol Rearrangement
Vicinal diols rearrange to carbonyl compounds under acid.
In-depth explanation of Pinacol Rearrangement
The pinacol rearrangement converts a vicinal diol, a diol with OH groups on adjacent carbons, into a carbonyl compound under acid conditions. One hydroxyl is protonated and leaves as water to form a carbocation, and a neighbouring group migrates from the adjacent carbon to this cation. The oxygen on the other carbon then stabilizes the new positive charge as an oxocarbenium ion, which is deprotonated to give a ketone or aldehyde. The driving force is the formation of this stabilized carbonyl product.
Going deeper: Pinacol Rearrangement
Key ideas: A 1,2-diol (vicinal) with acid loses water to give a carbocation, followed by a 1,2-alkyl or aryl shift and loss of H+ to give a ketone. Pinacol (2,3-dimethylbutane-2,3-diol) gives pinacolone (3,3-dimethyl-2-butanone). With unsymmetrical diols, the more stable carbocation forms first (tertiary or benzylic), then the group with higher migratory aptitude moves; the driving force is the oxocarbenium ion stability.
Common mistakes and connections: Students lose the correct carbon skeleton, forgetting which carbon bears the carbocation. Another error is thinking the reaction yields an alkene by simple dehydration. Links to Wagner-Meerwein shifts, carbocation stability and semipinacol rearrangements.
Visualization of Pinacol Rearrangement
Protonation and loss of water gives a carbocation, then an alkyl shift gives a stabilized oxocarbenium that loses H+ to the ketone. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Pinacol, 2,3-dimethylbutane-2,3-diol, rearranges under acid to give pinacolone.
Frequently asked questions about Pinacol Rearrangement
What is Pinacol Rearrangement?
Vicinal diols rearrange to carbonyl compounds under acid.
Is Pinacol Rearrangement a beginner, intermediate or advanced topic?
Pinacol Rearrangement is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Pinacol Rearrangement?
Study these earlier topics in Organic Chemistry first: Hydroboration-Oxidation, Baeyer-Villiger Oxidation, Beckmann Rearrangement.
What comes after Pinacol Rearrangement?
The next topics in Organic Chemistry are Wagner-Meerwein Rearrangement.
Can I practise Pinacol Rearrangement with quizzes?
Yes. The interactive lesson includes a self-check question on Pinacol Rearrangement, and the Organic Chemistry quiz draws on every topic in this area.
Where Pinacol Rearrangement fits in Organic Chemistry
Pinacol Rearrangement is topic 147 of 148 in Organic Chemistry.