Match List-I with List-II.
| List-I (Reactant and reagent) | List-II (Main organic product) |
|---|---|
| (A) Acetophenone, NaBH4 | (I) Ethylbenzene |
| (B) Acetophenone, Zn-Hg and concentrated HCl | (II) Propane |
| (C) Propanal, LiAlH4 followed by H2O | (III) 1-Phenylethanol |
| (D) Propanal, NH2NH2 followed by heating with KOH in ethylene glycol | (IV) Propan-1-ol |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-III, B-I, C-IV, D-II
The same carbonyl compound gives different products with different reducing agents. NaBH4 and LiAlH4 reduce the >C=O group to >CH–OH (an aldehyde gives a primary alcohol, a ketone a secondary alcohol). Clemmensen and Wolff–Kishner reductions remove the oxygen and reduce >C=O to >CH2.
(A) Acetophenone, NaBH4 — This matches (III) 1-Phenylethanol. A ketone is reduced to a secondary alcohol:
\( \displaystyle \ce{C6H5COCH3 + 2[H]} \xrightarrow{\ce{NaBH4}} \ce{C6H5CH(OH)CH3} \)
(B) Acetophenone, Zn-Hg and concentrated HCl — This matches (I) Ethylbenzene. This is the Clemmensen reduction; the C=O group becomes CH2:
\( \displaystyle \ce{C6H5COCH3 + 4[H]} \xrightarrow{\ce{Zn-Hg},\ \text{conc. }\ce{HCl}} \ce{C6H5CH2CH3 + H2O} \)
(C) Propanal, LiAlH4 followed by H2O — This matches (IV) Propan-1-ol. An aldehyde is reduced to a primary alcohol:
\( \displaystyle \ce{CH3CH2CHO + 2[H]} \xrightarrow[\text{(ii) }\ce{H2O}]{\text{(i) }\ce{LiAlH4}} \ce{CH3CH2CH2OH} \)
(D) Propanal, NH2NH2 followed by heating with KOH in ethylene glycol — This matches (II) Propane. This is the Wolff–Kishner reduction: the aldehyde first forms a hydrazone, which on heating with KOH in the high boiling solvent loses nitrogen:
\( \displaystyle \ce{CH3CH2CHO + NH2NH2 -> CH3CH2CH=NNH2 + H2O} \)
\( \displaystyle \ce{CH3CH2CH=NNH2} \xrightarrow[\text{ethylene glycol, heat}]{\ce{KOH}} \ce{CH3CH2CH3 + N2} \)
NCERT (2026-27 edition):
8.4 Chemical Reactions – “(i) Reduction to alcohols: Aldehydes and ketones are reduced to primary and secondary alcohols respectively by sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4) as well as by catalytic hydrogenation…”
“(ii) Reduction to hydrocarbons: The carbonyl group of aldehydes and ketones is reduced to CH2 group on treatment with zinc-amalgam and concentrated hydrochloric acid [Clemmensen reduction] or with hydrazine followed by heating with sodium or potassium hydroxide in high boiling solvent such as ethylene glycol (Wolff-Kishner reduction).”