Question

4 statements are given below. Identify the incorrect statement:

(A) Phenol has lower \( pK_a \) value than \( \text{p} \)-cresol.
(B) 2-Chlorophenol is more acidic than phenol.
(C) Ortho and para nitrophenols can be separated by steam distillation since \( \text{p} \)-Nitrophenol is more steam volatile than \( o \)-Nitrophenol.
(D) Phenol on reaction with \( \text{Cr}_2\text{O}_7^{2-} / \text{H}^+ \) yields a conjugated diketone.

• A. C
• B. B
• C. D
• D. A

Hint:

When working with acids and bases, remember that electron-donating groups make compounds less acidic, while electron-withdrawing groups increase acidity. Also, for steam distillation, compounds with lower boiling points or higher volatility are separated more easily.

Answer 1

The Correct Option is A

Let's analyze the statements: 
1. (A) Phenol has lower \( pK_a \) value than \( \text{p} \)-cresol: This statement is true because \( \text{p} \)-cresol is a weaker acid compared to phenol. 
The methyl group in \( \text{p} \)-cresol is an electron-donating group, which increases the electron density on the aromatic ring, making phenol less acidic than \( \text{p} \)-cresol. 
2. (B) 2-Chlorophenol is more acidic than phenol: This statement is true. The chlorine atom in 2-chlorophenol is an electron-withdrawing group that stabilizes the negative charge on the oxygen atom after deprotonation, thus making 2-chlorophenol more acidic than phenol. 
3. (C) Ortho and para nitrophenols can be separated by steam distillation since \( \text{p} \)-Nitrophenol is more steam volatile than \( o \)-Nitrophenol: This statement is incorrect. \( \text{p} \)-Nitrophenol has lower steam volatility compared to \( o \)-Nitrophenol due to the stronger intermolecular hydrogen bonding in \( \text{p} \)-nitrophenol, which makes it less volatile than \( o \)-nitrophenol. Therefore, they cannot be separated by steam distillation based on their volatility. 
4. (D) Phenol on reaction with \( \text{Cr}_2\text{O}_7^{2-} / \text{H}^+ \) yields a conjugated diketone: This statement is true. The reaction of phenol with \( \text{Cr}_2\text{O}_7^{2-} / \text{H}^+ \) results in oxidation of phenol, and the product formed is a conjugated diketone, which is a product of the oxidation of phenol. 
Thus, the incorrect statement is (C), and the correct answer is \( (A) \).