See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the reaction sequence: mCPBA is a peracid that performs epoxidation of alkenes, converting the C=C double bond into an epoxide with retention of the alkene's geometry (syn addition of oxygen across the double bond). Step 2 (H3O+) is acid-catalyzed ring opening of the epoxide. Step 2 - Epoxidation of 1,2-dimethylcyclopentene: The starting material is 1,2-dimethylcyclopentene (both methyl groups on the double bond). mCPBA adds an oxygen atom across the double bond in a syn fashion, giving 1,2-dimethylcyclopentene oxide (an epoxide). The oxygen bridges C1 and C2 from one face. Step 3 - Acid-catalyzed ring opening of the epoxide: Under acidic conditions (H3O+), the epoxide undergoes ring opening via an SN2-like mechanism with water acting as the nucleophile. The nucleophile attacks from the back side (anti) relative to the epoxide oxygen. Since the epoxide oxygen was added syn (from one face), the water attacks anti to that face, giving a trans (anti) diol product. Step 4 - Stereochemical outcome: For 1,2-dimethylcyclopentene oxide, acid-catalyzed ring opening gives the trans-1,2-diol with the two OH groups in a trans (anti) relationship to each other, and each OH is trans to the methyl on the same carbon. Because the ring is cyclopentane, the two OH groups end up on opposite faces of the ring (trans diol). The two methyl groups, originally on the double bond, end up one on each carbon with defined stereochemistry. Step 5 - Matching to options: - Option (b) shows a cis-diol (both OH groups on the same face), which would result from OsO4 or KMnO4 (syn dihydroxylation), not from mCPBA/H3O+. - Option (a) and (d) have incorrect stereochemical assignments for the methyl/OH arrangement. - Option (c) correctly shows the trans-diol: the two OH groups are on opposite faces of the cyclopentane ring, consistent with anti addition of water to the epoxide. The methyl groups and hydroxyl groups in option (c) reflect the correct trans relationship expected from epoxidation followed by acid-catalyzed ring opening. Therefore, the correct answer is C.