Chapter 9, Problem 9.55P

Interpretation Introduction

Interpretation:

The mechanisms of the two given reactions giving the same ${\text{S}}_{\text{N}}\text{2}$ product are to be drawn, and the product is to be determined. It is to be determined which of the two reactions is more efficient.

Concept introduction:

Primary alkyl halides tend to undergo an ${\text{S}}_{\text{N}}\text{2}$ reaction. The ${\text{S}}_{\text{N}}\text{2}$ mechanism is a single step, bimolecular reaction. The nucleophile attacks the electrophilic carbon in the substrate, forcing the leaving group to break off. The rate of the reaction and its efficiency depends on the nature of both the substrate and the nucleophile.

In case of the substrate, the relative rate of an ${\text{S}}_{\text{N}}\text{2}$ reaction changes with the type of carbon as ${\text{methyl > 1}}^{\text{o}}{\text{ > 2}}^{\text{o}}{\text{ > 3}}^{\text{o}}$ because of the increasing steric hindrance.

In case of the nucleophile, the steric hindrance is less important as the reaction center, i.e., the atom which donates the electron pair, is away from any bulky alkyl groups.

Sodium salts of alcohols are ionic compounds and tend to behave as a spectator ion ${\text{Na}}^{+}$ and the nucleophilic anion ${\text{RO}}^{-}$, where R is the alkyl group in the alcohol.