See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Hydroboration-oxidation is a syn-addition reaction that adds H and OH across a double bond with anti-Markovnikov regioselectivity. The boron attaches to the less substituted carbon, and the overall addition of H and OH is syn (both added to the same face). Step 1: Identify the substrate. The starting material is 1-methylcyclopent-1-ene, which has a trisubstituted double bond between C1 (bearing the methyl group) and C2. Step 2: Regioselectivity. In hydroboration, boron adds to the less hindered (less substituted) carbon. C2 is less substituted than C1 (which bears the methyl group). Therefore, boron adds to C2, and hydrogen adds to C1. Step 3: After oxidation (H2O2/HO-), the boron at C2 is replaced by OH with retention of configuration. So OH ends up at C2 (the less substituted carbon) - anti-Markovnikov product. Step 4: Stereochemistry. Syn addition means H and OH add to the same face of the double bond. Boron and H are delivered to the same face simultaneously. This gives a trans relationship between the CH3 group (which is on C1) and the OH group (on C2) when drawn on the cyclopentane ring, because the methyl is already on C1 and the H that adds to C1 comes from the same face as the BH3, giving the H at C1 and OH at C2 in a trans (anti) relationship relative to each other on the ring. Step 5: Evaluating options. Option (a) shows the cyclopentane product with CH3 and H at C1 (CH3 up, H on wedge meaning H comes toward viewer) and OH at C2 on a dash (going away from viewer), indicating a trans relationship between the H at C1 and OH at C2 - this is consistent with syn addition of BH3 followed by oxidation giving the trans alcohol product. Option (c) shows a cis relationship (both H at C1 and OH at C2 on wedge), which would correspond to anti addition - incorrect. Options (b) and (d) show incorrect connectivity or regiochemistry. Why other options fail: (b) lacks proper stereochemical depiction consistent with syn addition; (c) shows cis product which would result from anti addition (not hydroboration); (d) shows a dimethylcyclopentane which is a completely wrong product. Therefore, the correct answer is A.