Chapter 5.4, Problem 5.20P

Propose a mechanism for each of the following reactions:

Interpretation Introduction

Interpretation:

Mechanism for the given transformation has to be proposed.

Explanation of Solution

Given reaction is,

Mechanism:

Looking into the reaction it is found that the nucleophile is a strong one namely hydroxide and the reactant has all the three important criteria to undergo ${\text{S}}_{\text{N}}\text{Ar}$ mechanism.  In the reactant, nitro group (electron withdrawing group) and chlorine (leaving group) are present ortho to each other.

First step is the attack of nucleophile on the carbon atom that bears that chlorine atom which is a leaving group resulting in formation of Meisenheimer complex.

The formed Meisenheimer complex has the following resonance structures.

Second step is the expelling of the leaving group to give the product.

As the given condition is basic, deprotonation takes place.

Under acidic condition the formed ion is protonated to give the product.  This is the reason for using acid in order to complete the reaction.

Complete mechanism can be given as shown below,

Mechanism for the given transformation is proposed.