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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3nc233

The compound shown has a ring bearing a basic site and a pyridine-type nitrogen. Select all the correct statements.

  1. AThe pyrrolidine-ring nitrogen is the more basic site in water
  2. BThe pyridine nitrogen lone pair lies in an sp2 orbital in the ring plane
  3. CThe pyrrolidine-ring nitrogen is sp2 hybridised and conjugated with the pyridine ring
  4. DProtonation at the pyridine nitrogen is preferred because it keeps the sextet intact and the nitrogen is sp2

Answer: A, B

The compound shown is nicotine. The saturated N-methylpyrrolidine nitrogen is a trialkylamine type with sp3 lone pair (conjugate acid pKa about 8), more basic than the pyridine nitrogen (about 3). The pyridine lone pair is indeed sp2 and in-plane, but sp2 character holds electrons tighter, so it is not the preferred site. The pyrrolidine nitrogen is sp3 and not conjugated.
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