Question

Increasing order of acidic strength among p-methoxy phenol (I), p-methyl phenol (II) and p-nitrophenol (III) is

• A. III, I, II
• B. II, I, III
• C. III, II, I
• D. I, II, III

Answer 1

The Correct Option is C

The question asks for the increasing order of acidic strength among three compounds: p-methoxy phenol (I), p-methyl phenol (II), and p-nitrophenol (III). To solve this, we need to understand how substituents on the phenol affect its acidity.

Phenol is acidic because it can release a proton (H₊) to form a phenoxide ion. The stability of this phenoxide ion determines the acidity of the phenol. Electron-withdrawing groups (EWGs) like nitro groups (-NO₂) increase acidity by stabilizing the negative charge on the phenoxide ion through resonance or inductive effects. On the other hand, electron-donating groups (EDGs) like methyl (-CH₃) and methoxy (-OCH₃) decrease acidity because they destabilize the phenoxide ion.

1. p-Nitrophenol (III): The nitro group is a strong electron-withdrawing group. It stabilizes the phenoxide ion by resonance, making p-nitrophenol the most acidic among the three.
2. p-Methyl phenol (II): The methyl group is a weak electron-donating group. It does not stabilize the phenoxide ion as much, making p-methyl phenol less acidic than p-nitrophenol.
3. p-Methoxy phenol (I): The methoxy group is an electron-donating group through resonance and inductive effects. It destabilizes the phenoxide ion more than the methyl group, making p-methoxy phenol the least acidic.

Therefore, the increasing order of acidic strength is: III, II, I, which indicates that p-nitrophenol is the most acidic, followed by p-methyl phenol, and p-methoxy phenol is the least acidic. This matches the provided correct answer.