See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: When toluene reacts with chlorine (Cl2), the reaction conditions determine where chlorination occurs. In the presence of light (hv), the reaction proceeds via a free radical mechanism. In the presence of a Lewis acid catalyst (e.g., AlCl3 or FeCl3), the reaction proceeds via electrophilic aromatic substitution (EAS), substituting on the ring. Step 1: Identify the reaction conditions. The question specifies 'in the presence of light,' which means photochemical/free radical conditions (hv). Step 2: Free radical chlorination under light. Light (hv) causes homolytic cleavage of Cl2 to generate chlorine radicals (Cl•). These radicals preferentially attack the benzylic position (the methyl group side chain) rather than the aromatic ring, because the benzylic radical intermediate is stabilized by resonance with the aromatic ring. Step 3: The benzylic C-H bond of the CH3 group is weaker and more reactive toward radical abstraction. The chlorine radical abstracts a hydrogen from CH3 to give a benzyl radical (C6H5-CH2•), which then reacts with Cl2 to give benzyl chloride (C6H5-CH2Cl) and another Cl• to continue the chain. Step 4: Product identification. The product is benzyl chloride (PhCH2Cl), which is option (c): a benzene ring with a -CH2Cl group attached. Why other options fail: - Option (a): Polychlorination of the ring at multiple positions would require EAS conditions, not free radical/light conditions; also adding Cl to ring carbons directly in this pattern is not what light promotes. - Option (b): ortho-chlorotoluene is an EAS ring substitution product, favored with Lewis acid catalyst, not with light. - Option (d): para-chlorotoluene is also an EAS ring substitution product, favored with Lewis acid catalyst, not with light. Therefore, the correct answer is C.