Question

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1,2 diols form carbonyl compounds via the Pinacol Rearrangement. Provide a stepwise mechanism, Details count; include all nonbonding electrons and formal charges!

Answer 1

Concepts and reason

The organic reaction is classified into four major types based on their mechanistic behavior (transformation to the product) are as follows:

1.Substitution reaction.

2.Elimination reaction.

3.Addition reaction.

4.Rearrangement reaction.

5.Oxidation-reduction.

Pinacol rearrangement:

It is also known as Pinacol-Pinacolone rearrangement. In this rearrangement, 1,2-diols are transformed to carbonyl compounds as ketones in the presence of acid catalyst and heat.

Arrow pushing mechanism in chemistry:

An arrow pushing is a technique to indicate the movement of electrons in the organic reaction mechanisms.

Fundamentals

Carbocations:

A Carbocation is an organic intermediate ion which refers to the carbon atom bearing a single positive charge. Instead of four bonds, the positive-charged carbon contains only three bonds. These intermediates are unstable but very reactive.

The stability of carbocation:

Tertiary carbocation is a more stable carbocation because it is surrounded by three electron donating methyl groups to stabilize it.

Arrow pushing rule:

The double-headed curved arrow used for a pair of electrons indicates the movement of an electron pair from electron source to electron sink.

Double head arrow

In an acid catalyzed dehydration reaction, a vicinal diols undergoes elimination of water to form a ketone.

Ans:

Stepwise mechanism for 1,2 diols that form carbonyl compounds via the Pinacol rearrangement: