See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 – Identify the substrate. The alkene shown is 8a-methyl-3,4,4a,5,6,7,8,8a-octahydronaphthalene with an exocyclic double bond (=CH2) at the ring junction, i.e., the CH2= group is attached to the C8a ring-junction carbon which also bears a CH3 group on a wedge bond. This is effectively a methylenedecalin. Step 2 – Hydroboration-oxidation mechanism. HB adds in a syn (cis) fashion across the double bond (anti-Markovnikov, syn addition). Boron goes to the less hindered face of the exocyclic =CH2, and H goes to the same face simultaneously. The subsequent oxidation (H2O2/NaOH) replaces B with OH with retention of configuration. Step 3 – Stereochemical analysis. The exocyclic =CH2 is at the ring junction carbon. The CH3 is on a wedge (coming toward viewer, axial on top). Boron can approach from either the top face (same side as CH3, i.e., syn to CH3) or the bottom face (opposite to CH3). Both faces are possible, giving two diastereomeric alcohols. Step 4 – Determining the products. Because hydroboration is syn addition and the carbon bearing the new CH2OH group becomes a new stereocenter: - Attack from the bottom face (opposite to CH3 wedge): B adds to the bottom face of CH2, H goes to ring junction from bottom → OH ends up on the bottom face (dash), H at the new –CH2– position. This gives a product where the –CH2OH becomes –CH2– with OH configuration corresponding to bottom-face delivery. Looking at the drawn structures, this corresponds to structure III (H on dash, OH on wedge at the exocyclic carbon, consistent with one diastereomer). - Attack from the top face (same side as CH3): OH ends up on the top face (wedge direction). This corresponds to structure V (both H and OH on dash, i.e., the other diastereomer). Step 5 – Why other options fail. Options I, II, IV, and VI show incorrect stereochemical relationships at the ring junction or the hydroxyl-bearing carbon inconsistent with syn addition from either face of this specific methylenedecalin system. The trans-decalin framework with the defined CH3 wedge restricts which faces are accessible and what the resulting stereochemistry must be, ruling out pairs (a), (b), and (c). Step 6 – Conclusion. The two products of hydroboration-oxidation are III and V, representing syn addition of –OH and –H to the two faces of the exocyclic double bond. Therefore, the correct answer is D.