Chapter 15.SE, Problem 52AP

Interpretation Introduction

Interpretation:

Given that the substitution reaction of toluene with Br₂ can, in principle, lead to the formation of three isomeric bromotoluene products. In practice, however, only o- and p-bromotoluene are formed in substantial amounts. The meta isomer is not formed. The structures of three possible carbocation intermediates are to be drawn and the predominance of ortho and para products over the meta product is to be explained.

Concept introduction:

When a monosubstituted benzene is subjected to electrophilic substitution reaction, the electrophile in principle can get substituted in any of the three positions, ortho, meta and para. Which isomer will be formed predominantly depends on the stability of the allylic intermediate formed by the attack of the electrophile on the benzene ring. The more stable intermediate will yield the products.

To draw:

The structures of three possible carbocation intermediates formed during the substitution reaction of toluene that leads to the formation of o-, p- and m-bromotoluenes.

To explain:

The observation when toluene reacts with bromine the ortho and para products are formed predominantly than the meta product.