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JEE Advanced levelSingle correct optionDifficulty 3 of 3nc124

1.0 mole of 4-(aminomethyl)aniline, (the two groups are para to each other), is treated with exactly 1.0 mole of dilute . The main site of protonation is

  1. Athe aromatic nitrogen, because it is attached directly to the ring
  2. Bboth nitrogens equally, because both are primary amino groups
  3. Cthe aliphatic nitrogen, because its lone pair is not delocalised and it is a much stronger base (pKb about 4.7 against about 9.4)
  4. Dthe benzene ring carbon para to the amino group, giving a sigma complex

Answer: C

The benzylic nitrogen is a typical alkylamine-type base with its lone pair localised (benzylamine pKb about 4.7). The aromatic nitrogen lone pair is delocalised into the ring (aniline pKb about 9.4), so it is about times less basic. One equivalent of acid therefore protonates the aliphatic nitrogen first.
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