Question

Given below are the four isomeric compounds \(P, Q, R, S\):
\(P\): Aromatic compound containing an \(-\mathrm{OH}\) group 
\(Q\): Aromatic compound containing an \(-\mathrm{CHO}\) group (aldehyde) 
\(R\): Aromatic compound containing a ketone group 
\(S\): Aromatic compound containing a ketone group Identify the correct statements from below: 
[A.] \(Q, R\) and \(S\) will give precipitate with \(2,4\)-DNP. 
[B.] \(P\) and \(Q\) will give positive Baeyer’s test. 
[C.] \(Q\) and \(R\) will give sooty flame. 
[D.] \(R\) and \(S\) will give yellow precipitate with \(I_2/\mathrm{NaOH}\). 
[E.] \(Q\) alone will deposit silver with Tollens’ reagent. Choose the correct option.

• A. A, B, D and E only
• B. C and E only
• C. A and E only
• D. A, C and E only

Hint:

Remember: Tollens’ test is specific for aldehydes, while \(2,4\)-DNP reacts with all aldehydes and ketones.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
We need to evaluate the chemical tests for different functional groups:
- 2,4-DNP: Tests for carbonyl groups (aldehydes and ketones).
- Bayer's Test (\( \text{KMnO}_4 \)): Tests for unsaturation (C=C).
- Sooty Flame: Indicates aromatic compounds.
- Iodoform Test (\( \text{I}_2/\text{NaOH} \)): Tests for methyl ketones (\( \text{R-CO-CH}_3 \)) or alcohols like \( \text{R-CH(OH)CH}_3 \).
- Tollen's Test: Tests for aldehydes.
Step 2: Detailed Explanation:
- Statement A: Q (aldehyde), R (ketone), and S (ketone) are all carbonyl compounds. They will react with 2,4-Dinitrophenylhydrazine to form coloured precipitates. (Correct)
- Statement B: P and Q have carbon-carbon double bonds. They should give a positive Bayer's test. (Note: In some competitive exams, specific constraints might apply, but chemically this is true).
- Statement C: All compounds (P, Q, R, S) are aromatic as they contain a phenyl group (\( \text{Ph} \)). They will burn with a sooty flame. Thus, the statement that Q and R give a sooty flame is factually correct. (Correct)
- Statement D: R is propiophenone (\( \text{Ph}-\text{CO}-\text{CH}_2\text{CH}_3 \)), which is NOT a methyl ketone. S is benzyl methyl ketone (\( \text{Ph}-\text{CH}_2-\text{CO}-\text{CH}_3 \)), which IS a methyl ketone. Only S gives the iodoform test. (Incorrect)
- Statement E: Q is cinnamaldehyde, which is the only aldehyde in the set. Aldehydes reduce Tollen's reagent to metallic silver. (Correct)
Looking at the choices, the combination A, C, and E is the most robust set of correct statements provided.
Step 3: Final Answer:
The correct statements are A, C and E only.