Question

Explain the following:

Toluene on treatment with Cl₂ in sunlight gives benzyl chloride, whereas when treated with Cl₂ in dark gives o-chlorobenzene and p-chlorobenzene.

Answer 1

In sunlight, Cl₂ undergoes homolytic cleavage to form free radicals, so toluene undergoes free-radical side-chain chlorination, giving benzyl chloride. In the dark, Cl₂ forms Cl⁺ (electrophile), so toluene undergoes electrophilic aromatic substitution to form o- and p-chlorotoluene.