Answer: -NO 2 group withdraws electrons from nitrogen through conjugation.
- A -NO<sub>2</sub> group withdraws electrons from nitrogen through conjugation
- B Its higher molecular weight reduces the lone pair's reactivity
- C Greater steric hindrance from the para-substituent blocks protonation
- D It forms additional hydrogen bonds that immobilise the lone pair
Correct answer: A. -NO<sub>2</sub> group withdraws electrons from nitrogen through conjugation
Explanation: The strong electron-withdrawing -NO<sub>2</sub> group at para position withdraws electron density from N through resonance, drastically reducing basicity.
In aniline, the nitrogen's lone pair is pulled into the benzene ring through resonance, leaving less electron density available to accept a proton - which is why aniline is a much weaker base than methylamine, where the lone pair is fully available.
Concept context
Nitrogen-containing organic compounds. Covers classification (primary, secondary, tertiary), basicity comparison, preparation methods, and reactions including diazotization and coupling, key for understanding dyes and pharmaceuticals.