Nitrogen-substituted carbocations reactivity

The electron-withdrawing nitrogen atom makes the intermediate obtained from electrophilic aromatic substitution of pyridine less stable than the carbocation intermediate obtained from electrophilic aromatic substitution of benzene. Pyridine, therefore, is less reactive than benzene. Indeed, it is even less reactive than nitrobenzene. (Recall from Section 19.14 that an electron-withdrawing nitro group strongly deactivates a benzene ring toward electrophilic aromatic substitution.)... 

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