Question

Which of the following is correct decreasing order of acidic strength for the compounds listed below?
I: p-chlorophenol, II: p-Cresol, III: p-nitrophenol, IV: p-methoxyphenol.

• A. II \(>\) IV \(>\) I \(>\) III
• B. I \(>\) II \(>\) III \(>\) IV
• C. III \(>\) I \(>\) II \(>\) IV
• D. IV \(>\) III \(>\) I \(>\) II

Hint:

Electron withdrawing groups raise acidity of phenol and electron donating groups lower it.

Answer 1

The Correct Option is C

Step 1: Approach:
Compare the stability of the four phenoxide ions. The more the charge is spread out or pulled away, the stronger the parent acid.

Step 2: Ranking:
Nitro group pulls electron density through the ring by resonance as well as induction, which is the best stabiliser. Chloro pulls by induction only. Methyl pushes electron density into the ring mildly. Methoxy pushes more strongly through lone pair donation, so its phenoxide is least stable.

Step 3: Result:
Acidity: nitro > chloro > methyl > methoxy, i.e. III > I > II > IV, option C. Options A, B and D place a donor group first or the nitro compound at the wrong spot.

Final Answer:
The decreasing order of acidity is III > I > II > IV, option (C). \[ \boxed{\text{III} > \text{I} > \text{II} > \text{IV}} \]