See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

In nucleophilic aromatic substitution (SNAr), the rate depends on how well electron-withdrawing groups (EWGs) stabilize the Meisenheimer complex intermediate. EWGs at ortho and para positions to the leaving group (Br) provide direct resonance stabilization of the negative charge in the Meisenheimer complex, making those positions most effective. Meta-positioned EWGs only provide inductive stabilization, which is weaker. Step 1 - Identify the positions of NO2 relative to Br (the leaving group) in each compound: - Compound 1: one NO2 ortho to Br → one ortho activating group - Compound 2: two NO2 groups both meta to Br → only inductive effect, no resonance stabilization of Meisenheimer complex - Compound 3: three NO2 groups at ortho (×2) and para (×1) to Br → maximum resonance stabilization (2 ortho + 1 para) - Compound 4: two NO2 groups, one ortho and one para to Br → two resonance-stabilizing groups Step 2 - Rank by number and position of activating EWGs for SNAr: - Compound 3 has the most EWGs in ortho/para positions (2 ortho + 1 para = 3 total, all resonance-active) → fastest - Compound 4 has two EWGs in ortho/para positions (1 ortho + 1 para) → second fastest - Compound 1 has one EWG in ortho position → third - Compound 2 has two EWGs but both meta → only inductive stabilization, weakest activation → slowest Step 3 - Order: 3 > 4 > 1 > 2 Step 4 - Check against options: (a) 3 > 4 > 1 > 2 ✓ (b) 3 > 4 > 2 > 1 — incorrect, places meta-dinitro above mono-orthonitro (c) 2 > 1 > 4 > 3 — completely reversed (d) 4 > 3 > 2 > 1 — incorrect ordering Therefore, the correct answer is A.