Q72 (2024)
Compound $P (C_8H_8O)$ gives a red orange precipitate with 2,4-DNP reagent and it does not reduce Fehling's reagent. On drastic oxidation with chromic acid, P gives an aromatic product Q that produces effervescence on treating with aq. $NaHCO_3$. Compounds P and Q, respectively, are:
- (1) Option A
- (2) Option B
- (3) Option C
- (4) Option D
### Related Formula
$$\text{Degree of Unsaturation} = C + 1 - \frac{H}{2} = 8 + 1 - 4 = 5$$
### Core Logic
1. 2,4-DNP positive $\implies$ Carbonyl group present.
2. Fehling test negative $\implies$ Ketone (Acetophenone).
3. Drastic oxidation of acetophenone ($C_8H_8O$) with chromic acid yields Benzoic acid ($Q = C_6H_5COOH$).
4. Benzoic acid gives effervescence with $NaHCO_3$ ($CO_2$ gas).
### Step 1: Conclusion
P is Acetophenone and Q is Benzoic Acid.
### Pattern Recognition
Positive 2,4-DNP + Negative Fehling = Aromatic Ketone (Acetophenone).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
