Hey, everyone. In our continued discussion on the nomenclature of heterocycles, we now take a look at the unsaturated ones. Here we're going to say that unsaturated heterocycles use common names for the parent chain and when it comes to these common names we're going to have to first memorize these initial three. Knowing these three will help us to remember the following ones. So here we have Furan, Thiophene, and Pyrrole.

Now, Furan is a 5-membered ring with oxygen replacing one of the carbons and we have 2 double bonds. For Thiophene, it's sulfur that replaces the carbon and again, 2 double bonds. And then finally, we have Pyrrole which has a nitrogen replacing our carbon with 2 double bonds. And remember, nitrogen ideally wants to make 3 bonds, so it has to be connected to a hydrogen as well. Here our memory tool would be, furious, thieves, petrol.

Furious for Furan, Thieves for Thiophene and petrol for Pyrrole. The next 3 are oxazole, thiazole, and imidazole. They're very similar to these first three that we learned, except now we have a nitrogen in the top right corner. The hint here is that they all have an imine involved if you really think about it. It's a carbon double bonded to a nitrogen.

So think about a carbon double-bonded to a nitrogen to form this side of these 3 heterocycles. Next, we have these next 2. And if you pay close attention, you can see that this portion of it resembles Furan and this portion here represents Thiophene. Now, benzo is just referring to the benzene ring attached to these rings. So that's why our names here would be Benzofuran.

And could you guess this one? Yes. That's a Thiophene. So this would be Benzothiophene. Again, remembering these 2 is based on us remembering the first three that we looked at.

Next, we have indole. Indole has this portion of itself which resembles pyrrole, And the memory tool is that pyrrole is indole. Alright. So indole has a portion of it that looks like pyrrole. Next, we have this structure here.

And if we look, we're going to say that this portion resembles imidazole. So here we're going to say this is Benzimidazole. Next, our last 3 we have pyridine, pyrimidine, and quinoline. With pyrimidine or pyridine actually, pyridine, we're going to see iodine means a cyclic compound with nitrogen. So think of pyridine as a benzene ring that has a nitrogen that has replaced one of our carbons.

Here, pyrimidine is just one step more. Here, we can think of it as an imine involved right here. So it's related to pyrimidine in that way. And then, finally, here we have quinoline, which we're going to say queen in line for a parade. Quinoline.

Queen in line, Quinoline. For parade, we have a portion of it that kind of resembles pyridine. And then we have an additional ring attached to it that also has alternating double and single bonds. Right? So here, remember what's in purple represents our most common ones that you need to commit to memory.

The other ones are common types of heterocycles. They're just seen less regularly. But again, we kind of remember how to name them if we can remember the first three heterocycles we reviewed. So we have Furan, Thiophene, and Pyrrole.