Chapter 22, Problem 22.29P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism for the formation of each given product is to be drawn. The major product of the reaction is to be predicted, and the reason for it to be explained.

Concept introduction:

Electrophilic aromatic substitution reactions generally take place under kinetic control. Electrophiles in electrophilic aromatic substitution reactions typically must be generated in situ from more stable precursors that can be added as starting materials. In the presence of Fe or ${\text{FeX}}_{\text{3}}$, halogenation occurs to yield halobenzene, where X is any halogen atom. This is called aromatic halogenation reaction. ${\text{FeX}}_{\text{3}}$ acts as a Lewis acid and complexes with molecular halogen in a coordination step.  In Step 2, heterolysis of the X-X bond takes place slowly, producing ${\text{X}}^{+}$ and ${\text{FeX}}_{\text{4}}{}^{\text{-}}$. Finally, Steps 3 and 4 make up the electrophilic aromatic substitution with ${\text{X}}^{+}$ as the electrophile. The extent of the formed electrophile depends on the stability of the ion. More stable electrophile will react with benzene.