Match List-I with List-II.
| List-I (Reaction of aldehydes and ketones) | List-II (Feature of the reaction) |
|---|---|
| (A) Addition of hydrogen cyanide | (I) Occurs very slowly with the pure reagent and is catalysed by a base |
| (B) Addition of sodium hydrogensulphite | (II) The addition compound is water soluble and gives back the carbonyl compound with dilute mineral acid or alkali |
| (C) Reaction of ketones with ethylene glycol in the presence of dry hydrogen chloride | (III) Gives cyclic products |
| (D) Addition of ammonia derivatives, H2N–Z | (IV) The equilibrium favours the product because the intermediate is rapidly dehydrated |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-I, B-II, C-III, D-IV
All four are nucleophilic addition (or addition-elimination) reactions of the carbonyl group. They differ in the nucleophile, the catalyst and what happens to the first addition product.
(A) Addition of hydrogen cyanide — This matches (I). Pure HCN adds very slowly. A base turns HCN into the cyanide ion, a stronger nucleophile, which adds readily to give a cyanohydrin:
\( \displaystyle \ce{HCN + OH^- <=> CN^- + H2O} \)
\( \displaystyle \ce{R2C=O + CN^- <=> R2C(O^-)CN} \xrightarrow{\ce{H^+}} \ce{R2C(OH)CN} \)
(B) Addition of sodium hydrogensulphite — This matches (II). The addition compound is water soluble, and dilute mineral acid or alkali gives back the carbonyl compound, so the reaction is used to separate and purify aldehydes:
\( \displaystyle \ce{R2C=O + NaHSO3 <=> R2C(OH)OSO2Na} \)
(C) Reaction of ketones with ethylene glycol in the presence of dry hydrogen chloride — This matches (III). Both OH groups of the glycol join the same carbon, so a five-membered ring, the ethylene glycol ketal, forms (scheme below the extract):
\( \displaystyle \ce{R2C=O + HOCH2CH2OH} \xrightarrow{\text{dry HCl gas}} \text{ethylene glycol ketal} + \ce{H2O} \)
(D) Addition of ammonia derivatives, H2N–Z — This matches (IV). The addition is reversible and acid catalysed; the intermediate quickly loses water to give >C=N–Z, and this pulls the equilibrium towards the product:
\( \displaystyle \ce{R2C=O + H2N-Z <=> R2C(OH)-NHZ} \)
\( \displaystyle \ce{R2C(OH)-NHZ -> R2C=N-Z + H2O} \)
NCERT (2026-27 edition):
8.4 Chemical Reactions – “(a) Addition of hydrogen cyanide (HCN): …This reaction occurs very slowly with pure HCN. Therefore, it is catalysed by a base and the generated cyanide ion (CN–) being a stronger nucleophile readily adds to carbonyl compounds to yield corresponding cyanohydrin.”
“The hydrogensulphite addition compound is water soluble and can be converted back to the original carbonyl compound by treating it with dilute mineral acid or alkali.”
“Ketones react with ethylene glycol under similar conditions to form cyclic products known as ethylene glycol ketals.”
“(e) Addition of ammonia and its derivatives: Nucleophiles, such as ammonia and its derivatives H2N-Z add to the carbonyl group of aldehydes and ketones. The reaction is reversible and catalysed by acid. The equilibrium favours the product formation due to rapid dehydration of the intermediate to form >C=N-Z.”
