See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: In electrophilic aromatic substitution (EAS), the rate and position of substitution on a benzene ring are governed by the substituents attached to it. Electron-donating groups (EDGs) activate the ring toward EAS, while electron-withdrawing groups (EWGs) deactivate it. When a molecule has two aromatic rings, EAS preferentially occurs on the more activated (electron-rich) ring. Step 1 – Analyze the substituent on the LEFT-HAND SIDE ring in each option: (a) Left ring is directly bonded to the carbonyl carbon of an ester (–C(=O)–O–). This is a strong EWG (via resonance and induction), strongly deactivating the left ring. EAS would prefer the RIGHT ring (phenoxy group is an EDG on the right ring). (b) Left ring is directly bonded to the carbonyl carbon of an amide (–C(=O)–NH–). The carbonyl is an EWG by resonance, deactivating the left ring. The right ring bears –NH– which is an EDG, making the right ring more reactive. EAS prefers the right ring. (c) Left ring bears –CH2–O– substituent. The oxygen of an ether is an EDG by resonance; however, when connected via CH2, the direct resonance donation to the left ring is attenuated (the CH2 insulates resonance). The right ring bears –O– directly, making it strongly activated. EAS prefers the right ring. (d) Left ring bears –CH2– group (a simple alkyl-like insulating methylene), which connects to a carbonyl that is on the RIGHT ring. The –CH2– group is weakly electron-donating (inductive, slightly activating) for the left ring, while the right ring bears –C(=O)– directly attached, which is a strong EWG deactivating the right ring. Therefore the LEFT ring (bearing only the –CH2– substituent, essentially a benzyl group that is relatively electron-neutral to slightly activated) is MORE electron-rich than the right ring. EAS preferentially occurs on the LEFT ring. Step 2 – Why other options fail: - Options (a) and (b): The left ring is directly attached to a carbonyl (ester or amide), making it strongly deactivated. EAS occurs on the right ring, not the left. - Option (c): The right ring has a directly attached –O– (strong EDG via resonance), making the right ring far more reactive than the left ring for EAS. - Option (d): The right ring has –C(=O)– directly attached (EWG), strongly deactivating it. The left ring, attached only through –CH2–, is comparatively electron-rich and is the preferred site for EAS. Step 3 – Conclusion: In compound (d), PhCH2C(=O)Ph (deoxybenzoin), EAS takes place preferentially on the left-hand side phenyl ring because it is less deactivated (the carbonyl is not directly on it, only separated by a –CH2– group), whereas the right phenyl ring is directly attached to the electron-withdrawing carbonyl and is deactivated. Therefore, the correct answer is D.