MolSynapsequestion bank
MolSynapse / Question bank / Amines and Aromatic Nitrogen Compounds / Basicity order among drawn amines and anilines
JEE Advanced levelSingle correct optionDifficulty 3 of 3nc230

The compound shown contains two nitrogen atoms. Which statement about its site of protonation and relative basicity is correct?

  1. AThe amino nitrogen is protonated, since an sp3-like nitrogen is always more basic than a ring nitrogen
  2. BThe ring nitrogen is protonated, but the amino group makes it less basic than pyridine by -I effect
  3. CThe ring nitrogen is protonated, because the cation is stabilised by donation from the amino nitrogen, so it is more basic than pyridine
  4. DNeither is protonated since both lone pairs are delocalised

Answer: C

The compound shown is 4-aminopyridine. Protonation at the ring nitrogen gives a cation in which the exocyclic NH2 lone pair delocalises onto the ring nitrogen (amidinium-like resonance). This strong +R stabilisation raises the pKa of its conjugate acid to about 9, far above pyridine (about 5). The amino lone pair is already conjugated with the ring, so it is not the site of protonation.
Practice Amines and Aromatic Nitrogen Compounds More on Basicity order among drawn amines and anilines
Previous questionNext question

More questions on Basicity order among drawn amines and anilines