Question

Nicotine has 2 different nitrogen atoms in its structure, explain which nitrogen will be more basic ?

Answer 1

Nicotine

There is a secondary nitrogen in an aromatic (pyridine) ring (a secondary amine), and a tertiary nitrogen in a pyrrolidine ring (a tertiary amine, not amide).

The sp2 nitrogen, like the one in the parent compound pyridine, has its lone pair in an sp2 orbital. Note that an sp^2 orbital has more s-character (33%) than does an sp^3 orbital (25%). Higher s-character means that the electrons are held closer to the nucleus. Being closer to the nucleus reduces the lone pair's basicity (ability to bond with H^+). That is why the sp^3 nitrogen in teh pyrrolidine ring is a stronger base than is the sp^2 nitrogen in the pyridine ring.