Hey, everyone. We're going to take a look at the rules for naming substituted unsaturated heterocycles. Here we're going to say that substituents are assigned location numbers with some additional rules. Remember, our naming convention is the location of substituent and then our parent. If we take a look at rule 1, rule 1 says that the heteroatom gets location 1.

So here, 1 and it gives substituents the lowest possible number. In this example, there are no substituents, so you just number it from either side: 1, 2, 3, 4, 5, or you could go the other way: 1, 2, 3, all the way around. Rule 2, the higher priority heteroatom gets location 1.

Remember, "open snacks nightly." Oxygen has higher priority than sulfur. Sulfur has higher priority than nitrogen. The second heteroatom gets the lowest or the next lowest number. So it's a 1, 2, 3. We're going this way towards the other heteroatom: 4, 5. So if more than one nitrogen is present, you start with the amine nitrogen. So, basically, the one that has a hydrogen attached. So here, rule 3, in bicyclic molecules, carbons at ring junctures or ring junctions are not numbered.

We're going to say the heteroatom gets location number 1. If we take a look here, we have two nitrogens within this bicyclic compound. And we're going to say that this is the amine nitrogen since it's the one with the hydrogen. And we're going to say 1, 2, 3. Now, our junctions are this carbon and this carbon.

Basically, think of them as the carbon bridges that connect the two rings together. We don't count them. So we go 1, 2, 3, skip, 4, 5, 6, 7. So this would have 7 in terms of the number. And these would be the three rules that we have to employ when dealing with these substituted, unsaturated heterocycles.