Pyridine is a 6-membered aromatic ring system ring. The N-atom contributes two electrons to the pi-system and also contains on sigma lone pair. The C-atoms in pyridine contain less pi-electron density compared to benzene as the result of the N-atom's higher electron density. Pyridine undergoes electrophilic aromatic substitution less readily compared to benzene. Pyridine undergoes nucleophilic aromatic substitution more readily compared to benzene.