An organic compound X has the molecular formula C8H8O. Match the observations on X in List-I with the conclusions drawn from them in List-II.
| List-I (Observation on X) | List-II (Conclusion) |
|---|---|
| (A) X forms an orange-red precipitate with 2,4-DNP reagent. | (I) X is a ketone, not an aldehyde. |
| (B) X does not reduce Tollens’ or Fehling’s reagent. | (II) X is an aldehyde or a ketone. |
| (C) X does not decolourise bromine water or Baeyer’s reagent. | (III) X is a monosubstituted aromatic compound. |
| (D) On drastic oxidation with chromic acid, X gives a carboxylic acid C7H6O2. | (IV) The high unsaturation of X is due to an aromatic ring, not a C=C bond. |
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 test answers one question about X. Put together, they show that X is acetophenone, C6H5COCH3.
(A) Orange-red precipitate with 2,4-DNP — This matches (II) X is an aldehyde or a ketone. 2,4-DNP reacts with the carbonyl group of both aldehydes and ketones, so this test alone cannot tell them apart.
(B) No reduction of Tollens’ or Fehling’s reagent — This matches (I) X is a ketone, not an aldehyde. These mild oxidising agents oxidise aldehydes but not ketones.
(C) No decolourisation of bromine water or Baeyer’s reagent — This matches (IV) The high unsaturation of X is due to an aromatic ring, not a C=C bond. C8H8O is highly unsaturated, yet X shows no C=C test, so the unsaturation must be in a benzene ring.
(D) Drastic oxidation gives C7H6O2 — This matches (III) X is a monosubstituted aromatic compound. C7H6O2 is benzoic acid, C6H5COOH, which has only one group on the ring:
\( \displaystyle \ce{C6H5COCH3} \xrightarrow{\ce{H2CrO4}} \ce{C6H5COOH} \)
NCERT (2026-27 edition):
8.4 Chemical Reactions (Example 8.4, Solution) – “(A) forms 2,4-DNP derivative. Therefore, it is an aldehyde or a ketone. Since it does not reduce Tollens’ or Fehling reagent, (A) must be a ketone. … The molecular formula of (A) indicates high degree of unsaturation, yet it does not decolourise bromine water or Baeyer’s reagent. This indicates the presence of unsaturation due to an aromatic ring.”
“Compound (B), being an oxidation product of a ketone should be a carboxylic acid. The molecular formula of (B) indicates that it should be benzoic acid and compound (A) should, therefore, be a monosubstituted aromatic methyl ketone. The molecular formula of (A) indicates that it should be phenyl methyl ketone (acetophenone).”