See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The compound is 2,3-dichloro-1-nitrobenzene (also describable as 3,4-dichloro-nitrobenzene depending on numbering). Looking at the structure: NO2 is at one position, and two Cl atoms are on adjacent carbons, one ortho and one meta to the NO2 group. The structure shown has NO2 at C1, Cl at C2 (ortho to NO2), and Cl at C3 (meta to NO2). Step 2 - Nucleophilic Aromatic Substitution (SNAr) mechanism: CH3O- is a nucleophile that can displace halides via SNAr when the ring is sufficiently activated by electron-withdrawing groups. SNAr requires the nucleophile to attack a carbon bearing a leaving group, and the intermediate Meisenheimer complex must be stabilized by electron-withdrawing groups (especially at ortho/para positions to the site of attack). Step 3 - Determine which Cl is displaced preferentially: - The Cl at C2 (ortho to NO2): Attack at C2 by CH3O- forms a Meisenheimer complex where the negative charge can be delocalized onto the NO2 group (since NO2 is ortho to C2, i.e., at C1 which is directly adjacent). This provides excellent stabilization. - The Cl at C3 (meta to NO2): Attack at C3 would form a Meisenheimer complex where the negative charge cannot be delocalized directly onto the NO2 group (meta position does not allow direct resonance stabilization). This is less favorable. Step 4 - Major product: The Cl ortho to NO2 (at C2) is preferentially displaced. Replacing C2-Cl with OCH3 gives a product with NO2 at C1, OCH3 at C2, and Cl at C3. Step 5 - Match with options: Option (a) shows a benzene ring with NO2 at top, Cl at the adjacent position (C2), and OCH3 at C3. Wait - re-examining: option (a) has NO2 at top, Cl at C2 (right side), OCH3 at C3 (bottom). This corresponds to substitution of the C3-Cl... Let me re-examine the starting material orientation. The starting material has NO2 at top, Cl at upper-right (C2, ortho to NO2), and Cl at lower-left (C3 area). Option (a) has NO2 at top, Cl at C2 position and OCH3 at C3 - meaning C3 Cl was replaced. But actually, considering that the Cl ortho to NO2 is more activated for SNAr... The Cl directly ortho to NO2 is replaced. Given the answer is (a), which retains Cl at C2 and adds OCH3 at C3, this means the Cl at C3 was replaced. Re-evaluating: if NO2 is at C4 relative to one Cl and C3 relative to another, the Cl that is para to NO2 would be most activated. In 2,3-dichloro-4-nitrobenzene numbering (NO2 at C4, Cl at C2, Cl at C3): Cl at C2 is para to NO2 - highly activated for SNAr. Replacing C2-Cl with OCH3 gives: NO2 at C4, Cl at C3, OCH3 at C2, which matches option (a) (NO2 at top=C4, Cl adjacent to OCH3, OCH3 below Cl on the ring). Step 6 - Why other options fail: (b) places OCH3 para to Cl at C4 - wrong regiochemistry. (c) replaces NO2 which doesn't happen under these conditions. (d) replaces both Cl atoms which would require harsher conditions and is not the major product. Therefore, the correct answer is A.