JEE Chemistry 2026 Question with Solution

Given: Compound 'P' undergoes reaction with NH₃ on heating to form Q. Then Q undergoes Hofmann bromamide reaction with KOH, Br₂ and the product further gives NC-CH₃ in carbylamine reaction with CHCl₃, KOH (alc), \Delta.

Find: The identity of compound 'P'.

The carbylamine reaction gives an isocyanide only from a primary amine. Since the final product is $CH_3NC$, the amine before this step must be $CH_3NH_2$.

In Hofmann bromamide degradation, an amide gives a primary amine with one carbon less than the parent amide. Therefore, to obtain $CH_3NH_2$, compound Q must be ethanamide, $CH_3CONH_2$.

Now Q is formed from 'P' by reaction with NH₃ followed by heating. This is the conversion of a carboxylic acid into its corresponding amide. Hence 'P' must be ethanoic acid, $CH_3COOH$.

Among the given structures, option 4 represents the corresponding carboxylic acid structure in the set shown. Therefore, the correct option is D.

Given: The final product is NC-CH₃.

Find: Which starting compound 'P' can produce it through the given sequence?

Step 1: Use the last reaction first. The reagents CHCl₃ and KOH (alc) with heat indicate the carbylamine reaction, which converts a primary amine into an isocyanide.

So,

Step 2: The previous reagents Br₂/KOH indicate the Hofmann bromamide reaction. In this reaction, the amide loses the carbonyl carbon and forms a primary amine with one less carbon.

Therefore,

Step 3: The first step uses NH₃ and heat, which converts a carboxylic acid into the corresponding amide.

Thus,

So the starting compound 'P' is the carboxylic acid corresponding to ethanamide. Hence the correct choice is option 4, that is D.