Chapter 10, Problem 10.37P

Interpretation Introduction

Interpretation:

It is to be explained how different products are formed when $\text{pentane-2, 4-dione}$ is treated with one molar equivalent of ${\text{Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ and bromoethane and with two molar equivalent of ${\text{NaNH}}_2$ and bromoethane.

Concept introduction:

The $\text{α}$ carbon (carbon adjacent to carbonyl carbon) having at least one proton can be converted to a nucleophile by deprotonation. The ${\text{pK}}_{\text{a}}$ of monoketone is about $\text{20}$, and that of diketone is $\text{8}\text{.9}$. Thus, the hydrogen attached to the carbon, which is flagged between two carbonyl carbons, is more acidic than the carbon, which is bonded to only one carbonyl carbon. This is due to greater resonance stabilization of carbanion in diketone than in monoketone. Greater the stabilization of negative charge on carbon, less nucleophilic it is. The reaction of primary alkyl halides proceeds via ${\text{S}}_{\text{N}}\text{2}$ mechanism. The good and less sterically hindered nucleophile favors ${\text{S}}_{\text{N}}\text{2}$ mechanism.