See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: An acid-base reaction involves proton transfer (Brønsted-Lowry) or electron pair donation/acceptance (Lewis). Grignard reagents (RMgX) and organolithium reagents (RLi) are strong bases/nucleophiles, and they react with proton donors (acids) via proton transfer, which is an acid-base reaction. Step 1 - Analyze option (a): The compound is a cyclohexene bearing a -CH2MgCl group (a Grignard reagent). When treated with water (H2O), the Grignard reagent acts as a base (the carbanion accepts a proton), and water acts as the acid. The reaction is: R-CH2MgCl + H2O → R-CH3 + Mg(OH)Cl. This is a classic Brønsted-Lowry acid-base (protonolysis) reaction. So (a) involves an acid-base reaction. Step 2 - Analyze option (b): An organolithium reagent (RLi) reacting with HBr in water. HBr is a strong acid and RLi is an extremely strong base. The reaction R-Li + HBr → R-H + LiBr is a proton transfer (acid-base) reaction. So (b) also involves an acid-base reaction. Step 3 - Analyze option (c): The 9-anthracenyl MgCl (Grignard reagent) reacting with deuterated benzoic acid (PhCOOD). The Grignard reagent (base) abstracts the deuteron from the O-D bond of the carboxylic acid (acid). This is: Ar-MgCl + PhCOOD → Ar-D + PhCOOMgCl. This is again a Brønsted-Lowry acid-base (protonolysis) reaction. Step 4 - Conclusion: All three reactions (a), (b), and (c) involve acid-base proton transfer reactions between organometallic compounds (strong bases) and proton donors (acids: water, HBr, deuterated carboxylic acid). Therefore all of these qualify. Why other options fail: Options (a), (b), and (c) individually are each correct, so none of them alone is the complete answer. The answer that encompasses all is (d). Therefore, the correct answer is D.