Q15-52E - Organic Chemistry (Mcmurry)

Question

The substitution reaction of toluene with Br2 can, in principle, lead to the formation of three isomeric Bromo toluene products. In practice, however, only o- and p-Bromo toluene are formed in substantial amounts. The meta isomer is not formed. Draw the structures of the three possible carbocation intermediates (Problem 15-51), and explain why ortho and para products predominate over meta products.

Step-by-Step Solution

Answer

Step 1: Substitution reaction

Substitution reactions are chemical reactions in which one functional group is replaced by other functional groups. These reactions sometimes form a mixture of ortho, meta, and para products.

Step 2: Substitution reaction of toluene with bromine

Toluene undergoes a substitution reaction with bromine in the presence of ${\text{FeBr}}_3$ to form 63 % of ortho Bromo toluene, 34 % of para Bromo toluene, and only 3 % of meta Bromo toluene.

Step 3: Possible carbocation intermediate

The intermediates formed in the ortho and para attack are most stable when compared to the intermediate formed by the meta attack. So, the meta isomer is not formed. The formation of carbocation intermediate is as represented as: