An acid-catalyzed and a base-catalyzed rearrangement of a β , γ -unsaturated carbonyl compound to a more stable α , β -unsaturated carbonyl compound has to be proposed. Concept introduction: The carbon which is adjacent to the carbonyl group is known as α -carbon , followed next by β -carbon and γ -carbon . The α , β -unsaturated carbonyl compounds are a type of carbonyl compounds where there is a double bond between the α and β -carbon . The β , γ -unsaturated carbonyl compounds are those where there is a double bond between the β and γ carbon. The α , β -unsaturated carbonyl compounds are most stable than the β , γ -unsaturated carbonyl compounds and hence rearrangement takes place in presence of either an acid or a base.

Question

A b,g-unsaturated carbonyl compound rearranges to a more stable conjugated a,b-unsaturated compound in the presence of either acid or base. a. Propose a mechanism for the base-catalyzed rearrangement. b. Propose a mechanism for the acid-catalyzed rearrangement.

Answer 1

Question

Chapter 18, Problem 61P

(a)

Interpretation Introduction

Interpretation: An acid-catalyzed and a base-catalyzed rearrangement of a β,γ-unsaturated carbonyl compound to a more stable α,β-unsaturated carbonyl compound has to be proposed.

Concept introduction: The carbon which is adjacent to the carbonyl group is known as α-carbon, followed next by β-carbon and γ-carbon. The α,β-unsaturated carbonyl compounds are a type of carbonyl compounds where there is a double bond between the α and β-carbon. The β,γ-unsaturated carbonyl compounds are those where there is a double bond between the β and γ carbon. The α,β-unsaturated carbonyl compounds are most stable than the β,γ-unsaturated carbonyl compounds and hence rearrangement takes place in presence of either an acid or a base.

(b)

Interpretation Introduction

Interpretation: An acid-catalyzed and a base-catalyzed rearrangement of a β,γ-unsaturated carbonyl compound to a more stable α,β-unsaturated carbonyl compound has to be proposed.

Concept introduction: The carbon which is adjacent to the carbonyl group is known as α-carbon, followed next by β-carbon and γ-carbon. The α,β-unsaturated carbonyl compounds are a type of carbonyl compounds where there is a double bond between the α and β-carbon. The β,γ-unsaturated carbonyl compounds are those where there is a double bond between the β and γ carbon. The α,β-unsaturated carbonyl compounds are most stable than the β,γ-unsaturated carbonyl compounds and hence rearrangement takes place in presence of either an acid or a base.

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