Answer: Lone pair on N is delocalised into the pi system of benzene ring, making it less available.
- A Lone pair on N is delocalised into the pi system of benzene ring, making it less available
- B Aniline's higher molecular weight directly increases its pKb value according to conventional understanding
- C A dominant steric effect from the ring blocks protonation of the nitrogen in routine practice
- D Aniline's lower molecular weight is what increases its acidic character overall in most cases
Correct answer: A. Lone pair on N is delocalised into the pi system of benzene ring, making it less available
Explanation: Resonance between N lone pair and the aromatic pi system in aniline reduces the electron density on N significantly.
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.