Chemistry - Aromatic Hydrocarbon Question with Solution | TestHub

The reaction of pyridine with HNO₃ and H₂SO₄ is a nitration reaction. However, pyridine is much less reactive towards electrophilic aromatic substitution than benzene due to the electron-withdrawing nitrogen atom. Furthermore, pyridine is protonated in the presence of strong acids like H₂SO₄, forming the pyridinium ion, which is even MORE deactivated towards electrophilic substitution.

The nitration of pyridine requires harsh conditions (high temperatures and concentrated acids) and occurs at the 3-position.

Reaction:

Pyridine + HNO₃/H₂SO₄ -> 3-nitropyridine

Mechanism:

1. Protonation of pyridine:

Pyridine reacts with H₂SO₄ to form pyridinium ion.

2. Electrophilic attack:

The nitronium ion (NO₂⁺), generated from the reaction of HNO₃ and H₂SO₄, attacks the 3-position of the pyridinium ion. The 3-position is favored due to resonance stabilization of the intermediate and is less sterically hindered than the 2- or 4- positions.

3. Deprotonation:

Loss of a proton restores aromaticity, yielding 3-nitropyridine.

The product is shown in option A.