See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Concept: Neighboring Group Participation (NGP) in nucleophilic substitution reactions. Step 1: Identify the substrate. The substrate is a compound with a cyclohexyl group attached to a 14C-labeled carbon (filled diamond), which is in turn attached to a carbon bearing the OTs leaving group (no label, marked with circle). The 14C label is on the carbon adjacent to the carbon bearing OTs. Step 2: Understand the labeling experiment. The 14C label is on one carbon and OTs is on the adjacent carbon. When RCO2H acts as nucleophile, two products are formed: one where the OCOR group is on the carbon that originally bore OTs (normal attack), and one where the OCOR group is on the 14C-labeled carbon (scrambled product). This scrambling of the label between the two carbons is the key observation. Step 3: Explain the mechanism via NGP. In SN-NGP (neighboring group participation), the oxygen atom of the ether/hydroxyl or the adjacent group acts as an internal nucleophile. Here, the phenyl ring or adjacent group participates: the leaving group (OTs) departs while the neighboring group forms a bridged intermediate (episulfonium-type or epoxide-like intermediate), creating a symmetrical or semi-symmetrical intermediate. This bridged intermediate can then be attacked by the external nucleophile (RCO2H/RCOO-) at either carbon, leading to two products with the label appearing at both positions. Step 4: Why not other options? - (a) SN1: SN1 would give a carbocation, and while it could give scrambling, the specific two-product pattern with label scrambling points to a defined bridged intermediate, not a free carbocation. - (b) SN2: SN2 gives clean inversion at one center only; would not produce two products with label scrambling. - (d) SN-Ar: Aromatic substitution is not relevant here as there is no substitution on the aromatic ring. Step 5: The two products observed correspond to nucleophilic attack at the two carbons of the bridged intermediate, which is characteristic of SN-NGP (neighboring group participation mechanism). Therefore, the correct answer is C.