Q35E - Organic Chemistry (Mcmurry)

Question

The herbicide acifluorfen can be prepared by a route that begins with reaction between a phenol and an aryl fluoride. Propose a mechanism.

Step-by-Step Solution

Answer

The mechanism of the given reaction is:

Step-by-Step Solution Step 1: Nucleophilic aromatic substitution reaction

A nucleophilic aromatic substitution reaction is a chemical reaction in which a nucleophile displaces a leaving group on the aromatic ring. The presence of the electron-withdrawing group increases the rate of nucleophilic aromatic substitution. This reaction generally follows the elimination addition or addition elimination pathway.

The nucleophilic aromatic substitution reaction does not follow an ${\mathrm{S}}_{\mathrm{N}}2$ reaction mechanism because of the steric hindrance of the benzene ring.

In the presence of an excellent leaving group, nucleophilic aromatic substitution may follow the ${\mathrm{S}}_{\mathrm{N}}2$ reaction mechanism.

Step 2: Meisenheimer complex

A Meisenheimer complex is a negatively charged intermediate formed by the attack of a nucleophile upon one of the aromatic ring carbon during the course of a nucleophilic aromatic substitution reaction. It is also a 1:1 reaction adduct between an arene carrying electron-withdrawing groups and nucleophiles.

Step 3: Proposed mechanism

The reaction is a nucleophilic aromatic substitution reaction. Here, the intermediate Meisenheimer complex is stabilized by the nitro group.

Mechanism of reaction