JEE Chemistry 2026 Question with Solution

Given: P gives positive Iodoform test and negative Tollen's test. On treatment with dilute acid, P gives Q. Compound Q gives both positive Tollen's test and positive Iodoform test.

Find: The correct structure of P.

A positive Iodoform test means the compound must contain either a methyl ketone group or a group that can produce it.

A negative Tollen's test means P is not an aldehyde.

After hydrolysis with dilute acid, Q gives positive Tollen's test as well as Iodoform test. Therefore Q must contain both an aldehyde group and a methyl ketone group.

From the solution, Q is identified as:

$$CH_3-CO-CH_2-CHO$$

This is a compound having both the required functionalities.

So P must be a protected form of this aldehyde, where the aldehyde is converted into an acetal, because acetals hydrolyse in dilute acid to regenerate aldehydes while remaining negative to Tollen's reagent.

Thus P is the acetal form corresponding to:

$$CH_3-C(=O)-CH_2-CH(OCH_3)_2$$

On hydrolysis:

$$CH_3-C(=O)-CH_2-CH(OCH_3)_2 \xrightarrow{H_3O^+} CH_3-C(=O)-CH_2-CHO + 2CH_3OH$$

This matches all the observations.

Therefore, the correct option is B.

Given:

• P gives Iodoform test positive.
• P gives Tollen's test negative.
• On dilute acid hydrolysis, P gives Q.
• Q gives both Tollen's and Iodoform tests positive.

Find: Which option represents P.

Step 1: Use the tests.

• Iodoform positive implies presence of a methyl ketone unit.
• Tollen's negative implies absence of a free aldehyde group in P.

Step 2: Analyze Q.

• Tollen's positive means Q contains an aldehyde.
• Iodoform positive means Q also contains a methyl ketone.

So Q must be a molecule containing both groups together.

Step 3: Infer the transformation. Dilute acid commonly hydrolyses acetals to aldehydes. Therefore P should be an acetal-protected aldehyde that still retains the ketone functionality.

That gives the structure:

$$CH_3-C(=O)-CH_2-CH(OCH_3)_2$$

which upon acid hydrolysis forms:

$$CH_3-CO-CH_2-CHO$$

Hence the option corresponding to the aldehyde-protected ketone is the correct choice.

The solution explicitly states that the correct option is B.