Chapter 18, Problem 18.47P

Interpretation Introduction

(a)

Interpretation:

The mechanism and product for the given reaction is to be drawn.

Concept introduction:

The carbonyl carbon is electrophilic in nature due to the electronegativity difference. The nucleophile adds the electrophilic carbon of the carbonyl group. Since water is amphoteric in nature, it can act as an acid as well as base depending on availability and the reaction condition. The reaction follows a different mechanism for an acid and a base catalyst. When the reaction is catalyzed by the acid, the first step of the reaction is always protonation of the carbonyl oxygen, which increases the electrophilicity of the carbonyl carbon. For a base-catalyzed reaction, the first step is the deprotonation of the nucleophilic species to enhance the nucleophilic character.

Interpretation Introduction

(b)

Interpretation:

The mechanism and product for the given reaction are to be drawn.

Concept introduction:

The carbonyl carbon is electrophilic in nature due to the electronegativity difference. The nucleophile adds the electrophilic carbon of the carbonyl group. The $\text{α,β}$ unsaturated aldehyde or ketone possesses two electrophilic centers – one is carbonyl carbon itself and second is the $\text{β}$ carbon of the compound. Due to the resonance, there are two possible attacks for the nucleophile. When nucleophile adds $\text{β}$ carbon of the carbonyl compound, it is called $\text{1, 4-addition}$ or conjugate addition, and it is a reversible addition to the carbonyl group as the carbonyl group is regenerated on acid or the protic workup. The reaction follows a different mechanism for acid and a base catalyst. When the reaction is catalyzed by the acid, the first step of the reaction is always protonation of the carbonyl oxygen, which increases the electrophilicity of the carbonyl carbon. For a base-catalyzed reaction, the first step is the deprotonation of the nucleophilic species to enhance the nucleophilic character. The conjugate base of the weak acid is a strong nucleophile. Under the basic condition, a weak acid is deprotonated easily.