JEE Chemistry 2026 Question with Solution

Given: Compound $A$ has molecular formula $C_8H_8O_2$. It reacts with acetophenone to give a single product in cross-aldol condensation, and with concentrated NaOH it gives a substituted benzyl alcohol as one of the products.

Find: The correct identity of compound $A$.

A compound that gives a substituted benzyl alcohol with concentrated NaOH is undergoing the Cannizzaro reaction. This reaction is shown by aldehydes that do not contain any $\alpha$-hydrogen.

So, compound $A$ must be an aromatic aldehyde without $\alpha$-hydrogen.

Now check the options:

• A: 4-methyl benzoic acid is a carboxylic acid, so it does not undergo Cannizzaro reaction.
• B: 2-hydroxy acetophenone is a ketone and contains $\alpha$-hydrogen, so it is not suitable.
• C: 4-hydroxy benzylaldehyde has a benzylic $-CH_2-$ group, so it contains $\alpha$-hydrogen and does not satisfy the Cannizzaro condition.
• D: 4-methoxy benzaldehyde is an aromatic aldehyde without $\alpha$-hydrogen, so it undergoes Cannizzaro reaction.

For cross-aldol condensation with acetophenone to give a single product, the partner compound should not have $\alpha$-hydrogen. This condition is also satisfied by 4-methoxy benzaldehyde.

Therefore, the chemically consistent answer is 4-methoxy benzaldehyde.

The solution shows an answer-key mismatch: it labels option A, but the working supports D.

So, the correct option is D.

Given: The clues are cross-aldol condensation with acetophenone giving a single product, and Cannizzaro reaction with concentrated NaOH.

Find: Which option satisfies both clues.

Use the Cannizzaro clue first. Only aldehydes without $\alpha$-hydrogen give this reaction.

Then use the cross-aldol clue. To obtain a single crossed product with acetophenone, the second carbonyl compound should not form its own enolate, so it should also lack $\alpha$-hydrogen.

Applying these conditions:

1. 4-methyl benzoic acid is not an aldehyde.
2. 2-hydroxy acetophenone is a ketone with $\alpha$-hydrogen.
3. 4-hydroxy benzylaldehyde contains benzylic hydrogens next to the aldehyde-bearing system, so it is not the intended Cannizzaro substrate.
4. 4-methoxy benzaldehyde is an aromatic aldehyde without $\alpha$-hydrogen and fits both observations.

Hence, option D is the defensible answer from the solution logic.