Match List-I with List-II
|
List-I (Name of the test/Reaction) |
List-II (Species) |
|
(A) Tollen's Test |
(I) \( Cu^{2+} \) and \( OH^- \) |
|
(B) Fehling's Test |
(II) \( Zn-Hg \) and \( HCl \) |
|
(C) Clemmensen reduction |
(III) \( 2[Ag(NH_3)_2]^+ \) and \( OH^- \) |
|
(D) Wolff Kishner reduction |
(IV) Hydrazine KOH/ethylene glycol |
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)-(II), (D)-(IV)
The list has two tests that tell aldehydes from ketones and two reductions of the carbonyl group to CH2. In the tests a mild oxidising agent oxidises the aldehyde to the carboxylate ion and is itself reduced; ketones are not oxidised by such mild reagents. In the reductions the >C=O group of an aldehyde or ketone becomes a >\( \ce{CH2} \) group, in acid (Clemmensen) or in base (Wolff-Kishner).
(A) Tollen’s Test — This matches (III) \(2[Ag(NH_3)_2]^+\) and \(OH^-\). Tollens’ reagent is ammoniacal silver nitrate. The diamminesilver(I) ion oxidises the aldehyde in alkaline medium and is reduced to metallic silver, which forms a silver mirror:
\( \displaystyle \ce{RCHO + 2[Ag(NH3)2]+ + 3OH- -> RCOO- + 2Ag v + 2H2O + 4NH3} \)
(B) Fehling’s Test — This matches (I) \(Cu^{2+}\) and \(OH^-\). Fehling’s solution (copper sulphate with alkaline sodium potassium tartrate) supplies \( \ce{Cu^{2+}} \) in alkaline medium. An aliphatic aldehyde reduces it to a red-brown precipitate of copper(I) oxide:
\( \displaystyle \ce{RCHO + 2Cu^2+ + 5OH- -> RCOO- + Cu2O v + 3H2O} \)
(C) Clemmensen reduction — This matches (II) \(Zn-Hg\) and \(HCl\). Zinc amalgam and concentrated hydrochloric acid reduce the carbonyl group to a methylene group:
\( \displaystyle \ce{R2C=O} \xrightarrow{\ce{Zn-Hg},\ \text{conc. }\ce{HCl}} \ce{R2CH2 + H2O} \)
(D) Wolff Kishner reduction — This matches (IV) Hydrazine KOH/ethylene glycol. The carbonyl compound first forms a hydrazone with hydrazine; heating the hydrazone with KOH in a high-boiling solvent such as ethylene glycol removes nitrogen and leaves a >\( \ce{CH2} \) group:
\( \displaystyle \ce{R2C=O + NH2NH2 -> R2C=NNH2 + H2O} \)
\( \displaystyle \ce{R2C=NNH2} \xrightarrow[\text{heat}]{\ce{KOH}/\text{ethylene glycol}} \ce{R2CH2 + N2} \)
Shortcut: (A)-(III) appears in Options (2) and (4); (C)-(II) then leaves only Option (2).