Pyridine And Its Reactions M. Sc. II S.M. Joshi College Prof. Pawar A.A.

Aromatic Six-Membered-Ring Heterocycles

Pyridine reacts like a tertiary amine: The pyridinium ion is a stronger acid than a typical ammonium ion Pyridine reacts like a tertiary amine:

Pyridine Is Aromatic The nitrogen lone pair is not released into the aromatic system because it is perpendicular to the  system. The nitrogen withdraws electrons by resonance, resulting in an electron-deficient ring system.

Pyridine undergoes electrophilic aromatic substitution at

The pyridine nitrogen is a meta director:

Pyridine is reactive toward nucleophilic aromatic substitution because of the presence of the electronegative nitrogen:

Pyridine undergoes nucleophilic aromatic substitution at C-2 and C-4:

If the leaving groups at C-2 and C-4 are different, the incoming nucleophile will preferentially substitute for the weaker base:

Bromination and Oxidation of Substituted Pyridine

Diazotization of Aminopyridine

The a-hydrogens of alkyl substituents can be removed by base to generate anionic nucleophiles: Pyridine a-hydrogen acidity is similar to that of ketone a-hydrogens

Quinoline and isoquinoline are ring-fused pyridine derivatives:

Reactions of pyridine-based anionic nucleophiles:

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