Chapter 22, Problem 22.57P

Interpretation Introduction

Interpretation:

The complete and detailed mechanism for the given reaction is to be drawn.

Concept introduction:

Aromatic species tend to react with electrophiles (${\text{E}}^{+}$) in an electrophilic aromatic substitution reaction instead of an addition reaction because electrophilic aromatic substitution preserves aromaticity. The general mechanism for an electrophilic aromatic substitution reaction on benzene consists of two steps. First, ${\text{E}}^{+}$ undergoes electrophilic addition to the aromatic ring to produce an arenium ion intermediate, which temporarily destroys the ring’s aromaticity. The first step of electrophilic aromatic substitution that is the addition of the electrophile is slow, so it is the rate-determining step of the reaction. Thus, the reaction is first order with respect to both the aromatic ring and the electrophile. Second, a proton (${\text{H}}^{+}$) undergoes electrophile elimination, which restores aromaticity and results in a substituted aromatic ring.