See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

## Step-by-step Solution: **Understanding the Reaction:** The substrate is a cyclohexane derivative with Br and CH₃ groups on adjacent carbons (geminal positions). This undergoes an $S_N2$ reaction with $OAf^-$ (likely acetate or similar nucleophile, written as $OAf^-$). **Key Point — Methyl Benzylic Carbonium Ion Stability:** The problem states that the methyl benzylic carbonium ion is the most stable carbocation. This means the reaction proceeds via an intermediate where the **benzylic position (the carbon bearing both Br and CH₃)** can form a stable carbocation. **Mechanism Analysis:** 1. **Carbocation Formation:** The Br leaves, and a carbocation forms at the carbon bearing both Br and the CH₃ group (the benzylic-like center in this bicyclic system). 2. **Nucleophile Attack:** $OAf^-$ (nucleophile) attacks this carbocation from the **opposite face** (backside attack in $S_N2$ context, but here it's carbocation-driven). 3. **Stereochemistry:** The nucleophile approaches and attacks the carbocation. Given the rigid bicyclic structure, the $OH$ group will attach **exo** (pointing outward from the ring system) at the position where Br was originally. 4. **Product Structure:** The OH replaces Br at the benzylic position while maintaining the CH₃ group. The stereochemistry places OH pointing **away** from the ring (exo position). **Why Option D is Correct:** Option D shows the OH group in the **exo** position (projecting upward) at the benzylic center, with the methyl group and hydrogen atoms correctly positioned on the cyclohexane ring. This reflects proper carbocation rearrangement and nucleophilic attack geometry. **Why others are wrong:** - **(A)** & **(B)**: Place OH at wrong positions (not at the benzylic carbon where Br was) - **(C)**: Shows OH in the endo position (wrong stereochemistry)