See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: OsO4 dihydroxylation is a syn-addition reaction. OsO4 adds both OH groups to the same face of the double bond simultaneously via a cyclic osmate ester intermediate. NaHSO3 (sodium bisulfite) is used to cleave the osmate ester and liberate the diol. Step 2 - Identify the starting material: The starting material is 1-methylcyclopentene, which has a trisubstituted double bond in a cyclopentene ring with one methyl group on the double bond. Step 3 - Syn dihydroxylation: OsO4 attacks the double bond from one face, delivering both OH groups syn (cis) to each other. For 1-methylcyclopentene, the two carbons of the double bond (C1 bearing the methyl group and C2) each receive one OH group. Since addition is syn, both OH groups end up on the same face of the cyclopentane ring. Step 4 - Product stereochemistry: The product is a cis-1,2-diol (syn diol). C1 has a methyl group and an OH, and C2 has a methyl group (from the starting alkyl substituent pattern - wait, 1-methylcyclopentene has CH3 on C1 of the double bond; C2 is unsubstituted with H's). Actually C1 gets OH and retains CH3, C2 gets OH. The syn addition means both OHs are on the same face. Step 5 - Analyzing option (b): Option (b) shows the cyclopentane ring with C1 having CH3 on a wedge and OH on a bold/dashed bond, and C2 having OH on a wedge and CH3 on a bold/dashed bond. This represents the cis (syn) diol product where both hydroxyl groups are added to the same face, consistent with OsO4 syn dihydroxylation of 1-methylcyclopentene. Step 6 - Why other options fail: - Option (a): Shows only one OH group, not a diol product - incorrect for dihydroxylation. - Option (c): Shows OH groups on opposite faces (trans diol), which would be the product of anti addition (e.g., mCPBA then ring opening), not OsO4 syn addition. - Option (d): Shows only one OH and lacks the second hydroxyl group on C2 properly; also shows H instead of OH at one carbon. Step 7 - Conclusion: OsO4/NaHSO3 gives syn (cis) dihydroxylation. The product is the cis-diol shown in option (b). Therefore, the correct answer is B.