Degrees of Unsaturation

Hey guys. And I'm going to talk about a topic called Index of Hydrogen Deficiency. And this is a topic that usually isn't covered in the first chapter of most textbooks. So you're probably thinking, Johnny, why are you teaching this to me? If I don't need to know it yet Well, because there's this other topic called Constitutional I Summers and that topic is much easier to understand if you already know the HD rules. So what I'm gonna do here is gonna jump a little bit forward and teach you something that you don't need to know yet because it's gonna make isom are so much easier to understand for this chapter. All right, let's go ahead and begin. So there's actually two different ways to compete, to compute the H d. And that is one structural, and the other one is with molecular formula. What I'm gonna do on this page is to show you the structural one, which is actually the easier one, and then we'll move on to molecular formula. So first of all, let's just talk about what is index of hydrogen deficiency. Well, what it has to do with is how unsaturated or saturated a molecule is So what's that word saturated? Well, a saturated molecule is any molecule that has many hydrogen as possible. And there's this formula that we can use in all chemistry to figure out if it has many hydrogen is possible. And that formula is maybe remember it from Gen. Kim. It's to end plus two where N is equal to the number of carbons. Okay, so I have my two in plus two rule, and what that's gonna do is it's gonna predict for me how maney hydrogen is. I need for my structure, for it to be fully saturated, meaning it has many hydrogen, as it can possibly hold. Okay, any molecule that has less than that number to M plus two is gonna be considered to be unsaturated. And these air words saturated and unsaturated, they might sound familiar to you. And that's because these are words we use actually within cooking. So saturated fat would actually be a fat fats. Are these long carbon chains? There would be this fat that has many hydrogen as possible. Okay. And unsaturated fat would be one that's missing a few hydrants. So it be wondering. OK, Johnny What makes carbons, Miss Hydrogen? Why would you be missing some? It turns out it only happens for two different reasons. Okay, so I'm gonna write this down. It happens for pie. Bonn's okay. Remember that pie bonds just have to do with double bonds or triple bonds. They both have pi bonds and then also rings. Rings are also going to take away some of the hydrogen for a molecule. Because what that means is that the end that one of the end is supposed to be ch three on the other end is supposed to be ch three. When you make a ring, they have to fuse together. So that means that now you have to make them ch two. So what I'm trying to say is that a ring actually takes some hydrogen away from the carbon structure. Okay?

So if we use to m plus two and in this case equals five. So we do, too. Times five plus two. And that would mean that I need to have 12. Hydrogen is in order to be fully saturated. So then I would go ahead and ask myself, Does this have 12 hydrogen? And if you count, what you find is that you have 10 11 12. Wow, Look at that. I actually do have 12 hydrogen, so that means that is this molecule saturated or unsaturated? This would be saturated. Okay. Okay, so that's the first thing. So now I just showed you a molecule. It's saturated now another way that you could have known that this was saturated. Besides, doing the formula is you could have also asked yourself, Okay, what makes things unsaturated? Will pi bonds and rings. Did this chain have any pie bonds in it? No, it's all single Bonds didn't have any rings. No. So also, by looking at that, you could have said, Oh, this is gonna be a saturated molecules. See, that's how this gets really easy.

And it turns out that this one would be two times six plus two. So it should have 14 hydrogen. But how many does it actually have? That's right, 12. Okay. And are you counted? Like everyone? Each one has to. So this one actually is 12. Hydrogen isn't missing any hydrogen. Yes, it's actually missing two hydrogen, and Kate does that make sense? So this would be considered unsaturated.

So, um, this was also the same formula two times six plus two. It should have 14 ages. But how Maney does it actually have? Well, if you think about bond line structure, there's only supposed to be one h in each of these positions. Meaning that I only have six. H is meaning that I'm actually missing. How many? Okay, I'm missing eight h is That's huge. So in the first one, I had all the h is possible. In the second one, I'm missing two and the third one is missing eight.

so we know that we can use the words saturated and unsaturated to describe this. But is there a way to compare these guys? So is there a way to say Okay, which one is Maura Unsaturated In which one is less unsaturated because they're both very different. And the answer is yes. What we do is we use the HD rules toe. Really? Be very be very explicit about which one is the most unsaturated Which one is the least, So the way that we do this is really easy. All we do is, um, that we say that one I h d is the equivalent of missing two hydrogen. So if you're missing two hydrogen, that would be the equivalent of one index of hydrogen deficiency. That's just like the conversion. Alright. And the way that this works is that a ring or a double bond is gonna count as one HD one I HD okay. And then a triple bond is gonna count as two HD okay, because if you think about a triple one has two pi bonds in it. So that would be too I HD all right. And really that is it. Now, instead of having to use that complicated formula. I mean, the formula isn't hard, but it's just a little tedious sometimes. Imagine if you had, like, 11 carbons or something and you're having to like, maybe use more, more times tables than just your fingers. Whatever. What I'm trying to say is that it can get tedious counting all those hydrogen out, So instead we used these rules.

All right. So the answer is that how maney double bonds did I have? 1234 How many rings did I have? One. Okay, All of these count exactly the same. So this is going to be five. I HD isn't that easy. Okay, that's five HD. That means how maney hydrants are missing so that this would be a saturated molecule. Well, then I would just multiply this by two. Because I said that one I h d equals two hydrogen. So that means that 10 h is are missing. Does that make sense? See how much easier that was than counting up each individual hydrogen? That would take forever. Okay. And you'd probably make some mistakes, too.

Alright, guys. So you're getting fast that this Just you know, this one had nitrogen is in it and oxygen in it. Does that matter for structures? Absolutely not. Okay, when you're just looking at a structure, it doesn't matter what the atom is. All we're looking for is double bonds and rings. So this is just gonna be one too three. So three I HD. And then what are we missing? Six hydrogen are missing.

a little bit tricky, but it wasn't that bad. This one is zero I HD because it has no double bonds and it has no rings. So that means how Maney Hye Jin's air missing zero. Which means what kind of molecule is this? This is actually saturated. Okay, because it already has the amount of the most amount of hydrogen that can does that kind of makes sense. So what? I just showed you guys right now is the easiest way to calculate HD because you just have to look at it and you have your answer right there when I'm gonna show you in the next video is how to calculate it with, um, if you're given molecular formula instead, which is a little bit different. Okay, If you have any questions about this, let me know.

When you're given a molecular formula to calculate HD, you don't have the same clues that you had. Let's say if it was a structure, if you remember, we could use pi bonds or rings to figure out how many hydrogen were missing from a molecule. But when you're just given a molecular formula, let's say like this example c four h seven c l. I have no clue if there's rings there. If there's double bonds there, I really all I have is the atoms. Okay, so for this, we're gonna have to use our own rule and our own formula because that's really the only way to solve it. Now, your professor may have used a different ruling class and in fact, most of the rules that have seen a different from mine the only reason have settled on this one because it worked for a lot of my students and they like it better. But if you have a rule that your professor taught you that you like better, please, by all means, use that one. Alright, but this is the way it works. Basically, we need to calculate I HD on the way we do that is by calculating the theoretical h is the way we do that is by using the formula to one plus two. Okay, so basically, we calculate to in plus two, then we subtract the actual number of eight. Hydrogen is okay, but the thing is that for this we don't just use hydrogen. We also take into consideration other atoms that might act as hydrogen equivalence. Okay, so, for example, on the one in calculating the number of hydrogen is in a molecule. I don't just look at h. I also look at exes. Do you remember what X is X would be the A halogen and that counts as one hydrogen for this For this formula, I count. How login And a hydrogen? Exactly the same. Okay, so then oxygen. What about if I see an oxygen in my compound? What do I count? That as actually account that as zero, I ignore it. Okay, so whenever you see oxygen in this compound, just ignore it. That doesn't go into your equation. Then how about nitrogen? Nitrogen is a special case. Nitrogen is actually going to count as negative one hydrogen for your overall compound. So that means that I'm not just counting. H is, I'm also counting all ha logins and all nitrogen, and I'm ignoring the oxygen's. All right, so then finally I get that number. That number is going to go here. This is gonna be number of h is total. Okay, then I'm gonna take that number, and I'm gonna divide it all by two, which is what I have here. And that's gonna be your eye HD. Okay, Now, I know that sounds a little bit complicated, but once you get going with it, it actually you can actually do it pretty fast.

Let's just go through it one step at a time. So the first thing I would do is I would say, how Maney carvings do I have I have to put that into to win. Plus two. Okay, What that's going to give me is that my theoretical H is should be 10 ages. That's the long I should have. Okay, now, let's calculate how many h is I actually have. Well, there seem to be seven. H is right there. So I know I haven't least seven, but I also have a chlorine. What is a chlorine? A coin is a halogen. So that means it's gonna be I'm actually gonna have eight hydrogen equivalence here, So I'm gonna say 10 minus eight, hydrogen. And now I'm going to divide all that by two. And that's gonna be my i HD. It's really it's not that bad. So that Xena equal to over to which is the same as one. I h d. Okay, so now I can use that information to figure out okay, if I have one HD, that means that I either have a double bond. Yeah, or what do I have? Just remember the things that, um, equal one I h d r a double bond or a ring. Isn't that cool? So now I know that in this molecule, even though I don't really know, structure is I know. At least I have a dull bond or ring because I'm missing two hydrogen. How? Don't know I'm missing two hydrogen. Because remember that one h d equals two hydrogen. That air missed, okay?

so according to to m plus two, What I should have gotten for my theoretical is 14 ages. Okay? How maney h is do I actually have? Well, I actually have seven, but then I have a nitrogen. What does nitrogen count us next year? It actually counts is a negative. That means instead of writing the number seven, I'm gonna write six, because basically that nitrogen is taking away one of the hydrogen. Okay, so now I have 14 minus six, divided by two. What is that going to give you that's going to give you four? I HD okay? And I'm not going to go over all the possibilities here because obviously that could be a lot of double bonds, a lot of rings, church, triple bonds, etcetera. But what's important to know is that now you can convert this into my HD. Now you know how to figure out the HD for a molecular formula

all right, so in this case, my carbons was seven, so it would be two times seven plus two, which would actually equal 16 ages. What I'm going to subtract from that is just the number 12. Why is that right? Because oxygen's don't count. Remember, I ignore the oxygen's so it's 16 minus 12 over to that equals to I H. D.