Hey, everyone. So in this video, we're going to take a look at electrophilic substitution reactions of pyridine. Now here we're going to say unlike the five-membered aromatic heterocycles, pyridine is significantly less reactive than benzene. And in fact, we're going to say that the ring itself is electron deficient. Now remember, nitrogen is more electronegative than carbon, so the electron density is pulled towards the nitrogen atom.

So, it's going towards it. This makes the ring more electron deficient and less likely to undergo electrophilic substitution reactions. Now, nitrogen also gets a positive charge under electrophilic substitution reactions. Here, the nitrogen itself, since this lone pair is not part of the pi system, can be protonated giving us NH⁺ here, and it's positive. Or if it's in the presence of a Lewis acid catalyst, it could actually interact with it.

This would help minimize the potential for Friedel-Crafts reactions. So we'd have our nitrogen forming a linkage with aluminum chloride. Again, aluminum, nitrogen is making four bonds with positive. Now we can say that activating groups can help pyridine undergo electrophilic substitution reactions more effectively. So, again, because of its nature of the heteroatom, this particular heterocycle is less reactive towards electrophilic substitution reactions.