Question

Identify the incorrect match with respect to compounds to be distinguished and reagent used

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

To distinguish aldehydes from ketones, remember these key tests: - Tollens' Test (Silver Mirror): Aldehyde (+), Ketone (-). - Fehling's/Benedict's Test (Red Precipitate): Aliphatic Aldehyde (+), Ketone (-). Brady's test is a general test for the carbonyl group (C=O) and is positive for both aldehydes and ketones.

Answer 1

The Correct Option is D

Step 1: Analyze Option (A) - Iodoform Test: Reagent: \( \text{I}_2 + \text{NaOH} \). This test detects the presence of \( \text{CH}_3\text{-CH(OH)-} \) group or \( \text{CH}_3\text{-CO-} \) group. - Ethanol (\( \text{CH}_3\text{CH}_2\text{OH} \)) has the \( \text{CH}_3\text{-CH(OH)-} \) group. It gives a positive Iodoform test (yellow ppt). - Methanol (\( \text{CH}_3\text{OH} \)) does not. Thus, they can be distinguished. Match is correct.
Step 2: Analyze Option (B) - Lucas Test: Reagent: Lucas Reagent (ZnCl$_2$ + HCl). Distinguishes primary, secondary, and tertiary alcohols based on turbidity time. - Ethanol is a $1^\circ$ alcohol (No turbidity at room temp). - tert-Butyl alcohol is a $3^\circ$ alcohol (Immediate turbidity). Thus, they can be distinguished. Match is correct.
Step 3: Analyze Option (C) - Reaction with Sodium: Reagent: Sodium metal (Na). Reacts with acidic hydrogen (terminal alkynes). - Propyne (\( \text{CH}_3-\text{C}\equiv\text{CH} \)) has an acidic terminal hydrogen. Reacts with Na to release \( \text{H}_2 \) gas. - But-2-yne (\( \text{CH}_3-\text{C}\equiv\text{C}-\text{CH}_3 \)) has no acidic hydrogen. No reaction. Thus, they can be distinguished. Match is correct.
Step 4: Analyze Option (D) - 2,4-DNP Test: Reagent: 2,4-Dinitrophenylhydrazine. This is a general test for the Carbonyl group (Aldehydes and Ketones). - Acetaldehyde (\( \text{CH}_3\text{CHO} \)) is an aldehyde. It gives an orange-red ppt. - Acetone (\( (\text{CH}_3)_2\text{CO} \)) is a ketone. It also gives an orange-red ppt. Since both give a positive test, 2,4-DNP cannot distinguish between them. (Tollens' or Fehling's reagent would be needed). Thus, the match is incorrect.