Chapter 9, Problem 9.5P

Interpretation Introduction

Interpretation:

It is to be determined if ${\text{H}}_{\text{2}}{\text{P}}^{\text{-}}$ is a strong or weak nucleophile. It is also to be determined if it will favor the ${\text{S}}_{\text{N}}\text{1}$ or ${\text{S}}_{\text{N}}\text{2}$ mechanism.

Concept introduction:

The distinction between strong and weak nucleophiles is empirical.

Generally, the nucleophiles that are charged (total charge -1) are considered to be strong nucleophiles while neutral nucleophiles are considered to be weak nucleophiles.

Strong, negatively charged nucleophiles tend to favour ${\text{S}}_{\text{N}}\text{2}$ reactions as the nucleophile attacks the carbon atom before the leaving group departs.

Weak, uncharged nucleophiles tend to favour ${\text{S}}_{\text{N}}\text{2}$ reactions since the nucleophile is not involved in the rate-determining step.