See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The substrate is a cyclohexane bearing (at C1) an acetyl group (methyl ketone, –COCH3), (at C2) a chloromethyl group (–CH2Cl), and (at C4) a methyl group on a wedge bond (stereodefined). Step 2 - Reaction with CH3MgBr (Grignard reagent): The Grignard reagent (CH3MgBr) acts as a nucleophile and attacks the carbonyl carbon of the acetyl group. This is a nucleophilic addition reaction (1,2-addition to the ketone). This addresses option (a): Nucleophilic addition occurs. Step 3 - Intermediate alkoxide formation: After the Grignard addition, the carbonyl carbon becomes a tertiary alkoxide (–C(CH3)2–O^-MgBr+). The molecule now has a tertiary alcohol (after workup) adjacent to the –CH2Cl group on the cyclohexane ring. Step 4 - Intramolecular nucleophilic substitution: The alkoxide oxygen (generated after Grignard addition, even before aqueous workup) is positioned to attack the –CH2Cl carbon intramolecularly via an SN2 mechanism, displacing chloride. This forms a cyclic ether (epoxide or oxetane ring fused to the cyclohexane). This addresses option (b): Nucleophilic substitution reaction occurs. Step 5 - Product analysis: The product is a bicyclic compound containing an oxygen bridge — specifically an oxabicyclic system where a three-membered or four-membered oxygen-containing ring is fused to the cyclohexane. The product shown has a fused bicyclic ether with gem-dimethyl substitution. The starting material has a defined stereocenter (C4 methyl on wedge), and the ring closure creates additional stereocenters. Since the molecule contains stereocenters that are not related by a mirror plane (no internal plane of symmetry), the product is chiral. This addresses option (c): Product obtained is chiral. Step 6 - Conclusion: All three statements are correct — the mechanism involves (a) nucleophilic addition of CH3MgBr to the ketone, (b) intramolecular nucleophilic substitution of the chloride by the alkoxide, and (c) the final bicyclic ether product is chiral due to the presence of stereocenters without a compensating symmetry element. Therefore, the correct answer is D.