Want you guys to do, we're going to do the first one as a worked example and what I want you guys to do is work with me, think through this. Where do we start with these 2 molecules and maybe let's just call this question, "What would we start to compare them?" First of all, it's saying how are they related? Are they identical? Are they constitutional or are they different? I know right away there's one answer choice that we can eliminate. What do you guys think? Which one can we eliminate right away? Identical. These are not identical compounds. One of them has a ring and one of them is a chain. There's no way that those are the same thing. Wouldn’t you agree? So we're just going to scratch out identical. Let's not even think about that.

Now what I want to do is I want to go through my flowchart. Okay. So the first thing I do is I count up non-hydrogen atoms and IHD (InIndex of Hydrogen Deficiency). Let's start off with non-hydrogen atoms. What I have here is carbon, oxygen, and fluorine. Would you guys agree? I also have hydrogens present, but remember I'm going to ignore those for now. How many carbons do I have in the first molecule? Good. I have 5. 1, 2, 3, 4, 5. How many oxygens do we have? 1. How many fluorines do we have? 1. Makes sense so far?

Now I'm going to do the same thing for the other one. Carbons, oxygens, fluorines. How many carbons do I have? Also, 5. How many oxygens do I have? 1, and fluorine is 1. So far, it looks like all the atoms are the same. So it looks like maybe these are constitutional isomers. But let's also count IHD (InIndex of Hydrogen Deficiency). Remember I have to count IHD. So the IHD of this first one, just remember when you have a structure, how do you count IHD? Remember that double bonds and rings equal 1 and triple bonds equal 2.

So in this case, what's my IHD? It's 1. Now let's take the IHD of the second compound. What's the IHD of the second compound? 0. Are these IHDs the same? It's 0 because there's no ring, no double bond, no triple bond. So are these IHDs the same? No. What that means is that remember what it means for an IHD? It means that you're missing 2 H’s. It means you're missing 2 H’s. So do these two compounds have the same number of hydrogens? No. One has fewer than the other. So what are these going to be? Different compounds. Because I got stuck right up here, if not exactly the same, they are different compounds. That's exactly what happened. They were not the same, so I had different compounds. Does that make sense?

Now, the reason that I went through this whole trouble of teaching you IHD is because, as our molecules get bigger, that's going to be even more and more helpful. Instead of having to count out every single hydrogen, we just use IHD, and it's so much easier.