Question

What is the correct order of acidity for the following compounds?

• A. P $>$ N $>$ Q $>$ M
• B. P $>$ Q $>$ N $>$ M
• C. N $>$ P $>$ M $>$ Q
• D. N $>$ P $>$ Q $>$ M

Hint:

Picric acid (\(\text{P}\)) is a unique phenol containing three nitro groups, making it extremely acidic (stronger than benzoic acid and many mineral acids).
Remembering that Picric acid is stronger than Benzoic acid (\(\text{P} > \text{N}\)) immediately allows you to narrow down to the correct option (A).

Answer 1

The Correct Option is A

To determine the correct order of acidity for the given compounds, we need to consider the structure of each compound and how substituents affect acidity. 

1. Identify the Functional Groups:
   • M: Phenol (–OH group)
   • N: Benzoic acid (–COOH group)
   • P: 2,4,6-Trinitrophenol (Picric acid, –OH with three nitro groups)
   • Q: o-Nitrophenol (–OH with one nitro group)
2. Acidity Order Based on Electron-Withdrawing Groups (EWG):
   • EWGs, such as nitro (–NO₂), increase acidity by stabilizing the negative charge on the anion formed after deprotonation.
3. Analysis:
   • P (Picric acid): The presence of three nitro groups makes it highly acidic.
   • N (Benzoic acid): Naturally more acidic than phenol due to the –COOH group.
   • Q (o-Nitrophenol): More acidic than phenol due to one nitro group.
   • M (Phenol): Least acidic among the given compounds.
4. Conclusion:
   • The correct acidity order is P > N > Q > M. This is because Picric acid has the most electron-withdrawing nitro groups, enhancing acidity significantly.