See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the substrate: The starting material is a cyclopentanol derivative (specifically, it appears to be a substituted cyclopentanol with a methyl group). From the stereochemical drawing, the compound is trans-2-methylcyclopentanol (or a related isomer), where CH3 and OH are on the cyclopentane ring with defined stereochemistry shown by wedge/dash bonds. Step 2 - Identify the reagent: POCl3 in pyridine is a classic reagent for E2-type elimination of alcohols. It converts the OH into a good leaving group (as a chlorophosphate ester, -OPOCl2), and pyridine acts as the base to promote E2 elimination. This reaction proceeds with an anti-periplanar requirement (syn elimination is also possible via E2 with the chlorophosphate). Step 3 - Mechanism: POCl3 reacts with the OH to form a chlorophosphate intermediate. Pyridine (or the displaced chloride) then acts as base in an E2 process. The key is which beta-hydrogen is anti-periplanar (or appropriately positioned) to the leaving group. Step 4 - Regiochemistry and stereochemistry: The substrate is trans-2-methylcyclopentanol. In POCl3/pyridine conditions, the elimination is predominantly E2 with syn-periplanar geometry (since the chlorophosphate is an excellent leaving group and the reaction can proceed via syn elimination). The more substituted alkene is favored (Zaitsev). Elimination toward the carbon bearing the methyl group gives 1-methylcyclopentene (the more substituted, more stable alkene). This corresponds to option (b). Step 5 - Why other options fail: - (a) 3-methylcyclopentene is the less substituted product and would be the minor product (anti-Zaitsev). - (c) Cyclohexene is a 6-membered ring product, which cannot form from a cyclopentanol substrate without ring expansion; this is incorrect. - (d) Shows a chloride-containing product, but POCl3/pyridine with an alcohol gives elimination (alkene), not substitution under these conditions (pyridine drives elimination). Step 6 - Conclusion: The major product is 1-methylcyclopentene, the more substituted alkene, consistent with option (b). Therefore, the correct answer is B.