Question

Which one of the following is the major product of the hydrogenation reaction given below? 

 

• A. A
• B. B
• C. C
• D. D

Hint:

Pd–C (palladium on carbon) selectively hydrogenates double bonds under mild conditions.
Aromatic rings are usually unaffected unless subjected to high temperature and pressure.

Answer 1

The Correct Option is B

Step 1: Identify the reaction conditions.
Hydrogenation in the presence of Pd–C (palladium on carbon) is a catalytic reduction that selectively reduces C=C double bonds in alkenes and aromatic rings, depending on the substrate.
Step 2: Analyze the substrate.
The given molecule is a benzodihydrofuran derivative with an aromatic ring and a partially unsaturated fused ring system. Hydrogenation under Pd–C in ethanol typically reduces the non-aromatic double bond(s) first — that is, the double bonds in the alicyclic ring, not the aromatic ring.
Step 3: Predict the product.
- The benzene ring remains intact (aromatic systems are stable under mild catalytic hydrogenation).
- The double bond in the fused ring gets reduced to a saturated system. Hence, the hydrogen atoms add across the C=C bond of the cyclohexene-type ring, yielding a fully saturated fused ring compound.
Step 4: Conclusion.
Thus, the major product is the saturated tetrahydrofuran derivative represented by option (A).