Match List-I (observation) with List-II (reason).
| List-I (Observation) | List-II (Reason) |
|---|---|
| (A) Direct nitration of aniline gives a significant amount of m-nitroaniline. | (I) Atmospheric oxidation |
| (B) Aniline, usually colourless, gets coloured on storage. | (II) Formation of the anilinium ion in the strongly acidic medium |
| (C) The activating effect of the –NHCOCH3 group is less than that of the –NH2 group. | (III) Resonance in the arenediazonium ion |
| (D) Arenediazonium salts are stable for a short time in solution at 273–278 K. | (IV) Interaction of the lone pair on nitrogen with the oxygen atom by resonance |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-II, B-I, C-IV, D-III
Each observation has its own cause. Two of them come from what happens to the nitrogen of aniline (an acid or the air acts on it); the other two are resonance effects, but in different species.
(A) Direct nitration of aniline gives a significant amount of m-nitroaniline. — This matches (II) Formation of the anilinium ion in the strongly acidic medium. In the nitrating mixture aniline is protonated, and the anilinium ion is meta directing:
\( \displaystyle \ce{C6H5NH2 + H+ -> C6H5NH3+} \)
Direct nitration also gives tarry oxidation products, but these do not explain the meta product.
(B) Aniline, usually colourless, gets coloured on storage. — This matches (I) Atmospheric oxidation. Arylamines are slowly oxidised by the air, and the oxidation products are coloured.
(C) The activating effect of the –NHCOCH3 group is less than that of the –NH2 group. — This matches (IV) Interaction of the lone pair on nitrogen with the oxygen atom by resonance. In acetanilide the lone pair is drawn towards the C=O oxygen, so it is less available to the ring.
(D) Arenediazonium salts are stable for a short time in solution at 273–278 K. — This matches (III) Resonance in the arenediazonium ion. The positive charge of the –N2+ group is spread over the benzene ring, so the ion lasts for a short time in the cold. Alkyldiazonium salts have no such ring and are highly unstable.
NCERT (2026-27 edition):
9.6 Chemical Reactions – “Moreover, in the strongly acidic medium, aniline is protonated to form the anilinium ion which is meta directing. That is why besides the ortho and para derivatives, significant amount of meta derivative is also formed.”
“The lone pair of electrons on nitrogen of acetanilide interacts with oxygen atom due to resonance…” “Therefore, activating effect of –NHCOCH3 group is less than that of amino group.”
9.5 Physical Properties – “Aniline and other arylamines are usually colourless but get coloured on storage due to atmospheric oxidation.”
II. Diazonium Salts – “Primary aliphatic amines form highly unstable alkyldiazonium salts (refer to Section 9.6). Primary aromatic amines form arenediazonium salts which are stable for a short time in solution at low temperatures (273-278 K). The stability of arenediazonium ion is explained on the basis of resonance.”