JEE Chemistry 2026 Question with Solution

Given: The compound A on hydrogenation with $2H_2$ / $\text{Pt}$ gives the fully saturated fused bicyclic hydrocarbon, and on oxidation with $KMnO_4$ and heat gives a cyclohexane dicarboxylic acid along with oxalic acid.

Find: The correct structure of A.

Identify principle: Catalytic hydrogenation with $2H_2$ means that A contains two $\pi$ bonds. Strong oxidation with $KMnO_4$ cleaves the unsaturation and converts the suitable carbon fragments into carboxylic acids.

From the reaction scheme, hydrogenation produces decalin, so A must be an unsaturated fused bicyclic precursor of decalin containing exactly two double bonds.

The oxidation product shown is a cyclohexane ring bearing two adjacent $-COOH$ groups together with oxalic acid. This pattern is obtained when both double bonds are present in the same ring, because oxidative cleavage opens that ring to give a vicinal dicarboxylic acid fragment and the remaining two-carbon fragment is oxidized to oxalic acid.

Among the given structures, only option B has both double bonds in one ring of the fused bicyclic system and also consumes exactly $2H_2$ on complete hydrogenation to decalin.

Therefore, the correct option is B.

Given: Oxidation is carried out with $KMnO_4$ under strong conditions.

Find: Which option matches the observed cleavage products.

The provided hint states that strong oxidation converts benzylic or unsaturated carbon fragments into carboxylic acids. Here, the drawn product is not a simple monoacid; it is a dicarboxylic acid attached to a cyclohexane framework, plus oxalic acid as a separate fragment.

So we reject structures in which the two double bonds are distributed across both rings in a way that would not generate the shown pair of oxidation fragments. The structure must place the unsaturation so that one ring is preferentially cleaved while the fused skeleton still retains one cyclohexane ring in the product.

Option B matches this requirement and also fits the hydrogenation condition:

Hence, A = option B.