Question

Why does pyridine not give Friedel Craft's reaction?

Answer 1

1. Friedel Crafts reactions are electrophilic substitution reactions in which compounds containing an aromatic ring are treated with an alkyl halide or acyl chloride.
2. Here the electron-deficient electrophile attacks the electron-rich aromatic ring and forms a substitution product.
3. Lewis acids like anhydrous aluminium chloride $\left({\mathrm{AlCl}}_3\right)$ and ferric chloride $\left({\mathrm{FeCl}}_3\right)$ are used as catalysts in this reaction.
4. If we see the resonating structure of pyridine it is as follows.

1. The aromatic ring in this case has less electron density as the aromatic ring has a positive charge in most of the resonating structures.
2. Due to this incoming electrophile is repelled by the aromatic ring as both are positively charged.
3. The lone pair of electrons present on the nitrogen atom which does not take part in resonance attacks the electron-deficient Lewis acid and forms an additional product.
4. Hence, pyridine doesn't give Friedel Crafts reaction.