Resonance Vs Induction
Mediumchemistry
In p-nitrophenol, nitro group reduces phenolic acidity via resonance or inductive effect?
Select the correct option:
Solution
Incorrect! Answer:
Increases acidity via −I and −R
- Acidity Concept: Acidity of phenol depends on the stability of the phenoxide ion formed after losing a proton (H+).
- Nitro Group (−NO2): It is a powerful electron-withdrawing group via two mechanisms:
- Inductive Effect (−I): Withdraws electrons through σ bonds.
- Resonance Effect (−R or −M): Withdraws electrons through the π system, especially from the para position.
- Effect on Phenoxide: The −NO2 group at the para position delocalizes the negative charge on oxygen more effectively, making the phenoxide ion more stable.
- Result: Increased stability of conjugate base leads to increased acidity.
- Check: p-nitrophenol is significantly more acidic than phenol (pKa 7.15 vs 10).
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About This Question
- Subject
- chemistry
- Chapter
- basic organic principles
- Topic
- resonance vs induction
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Increases acidity via −I and −R
- Acidity Concept: Acidity of phenol depends on the stability of the phenoxide ion formed after losing a proton (H+).
- Nitro Group (−NO2): It is a powerful electron-withdrawing group via two mechanisms:
- Inductive Effect (−I): Withdraws electrons through σ bonds.
- Resonance Effect (−R or −M): Withdraws electrons through the π system, especially from the para position.
- Effect on Phenoxide: The −NO2 group at the para position delocalizes the negative charge on oxygen more effectively, making the phenoxide ion more stable.
- Result: Increased stability of conjugate base leads to increased acidity.
- Check: p-nitrophenol is significantly more acidic than phenol (pKa 7.15 vs 10).
This medium difficulty chemistry question is from the chapter basic organic principles, covering the topic of resonance vs induction. It appeared in the 2025 exam.
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