See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Nucleophilic Aromatic Substitution (SNAr) requires activation of the aromatic ring by strong electron-withdrawing groups (EWG) ortho/para to the leaving group. Without such activation, aryl halides are essentially unreactive toward nucleophilic substitution under normal conditions. Step 1: Identify the substrate. The starting material is 4-chlorotoluene (1-methyl-4-chlorobenzene). The leaving group is Cl attached directly to the aromatic ring. Step 2: Assess reactivity toward nucleophilic aromatic substitution. For SNAr to occur, the ring must bear strong electron-withdrawing groups (e.g., -NO2, -CN, -CF3) ortho or para to the leaving group to stabilize the Meisenheimer complex intermediate. The methyl group (-CH3) at the para position is an electron-DONATING group, not an electron-withdrawing group. Step 3: Since the methyl group donates electron density into the ring, it destabilizes the Meisenheimer complex rather than stabilizing it. There is no EWG to activate the ring for nucleophilic attack by SH-. Step 4: Benzyne mechanism requires very harsh conditions (strong base, very high temperature) and is not applicable here under normal NaSH conditions. Step 5: SH- is not a radical reagent, so radical substitution is not operative here either. Step 6: SN2 substitution on an sp2 carbon of an arene is geometrically impossible under normal conditions. Conclusion: NaSH cannot displace Cl from 4-chlorotoluene because there are no activating electron-withdrawing groups on the ring. The reaction does not proceed. Why other options fail: - (a) would require replacement of ring Cl with SH - not possible without activation - (c) would require substitution at the benzylic CH3 - NaSH is not typically used for benzylic substitution and the methyl group here is directly on the ring (no benzylic CH2Cl present) - (d) would require replacement of ring Cl with SH on an unactivated ring - not feasible Therefore, the correct answer is B.