 So let's go over this last example. It says an unknown sample CXHY02 gives this mass spec write a molecular structure for the molecule. So the first thing that we want to do is identify the two major peaks, right? So which one is the parent ion real quick? The 100, of course. And the base peak? Forty-three. Forty-three. Okay. So the base peak is so tall because the fragment that it's identifying is the most what fragment? Stable fragment. Okay. So that's why it's so tall. And the parent peak, the parent mass, gives you the mass of what? The most fragment. The whole molecule. The whole molecule, the whole molecule, right? The cool thing about it is we have the mass of the whole molecule, 100, right? And we know that there's two oxygens in there. So what can we do starting out? You can take out the two oxygens. Yeah. Take out those two oxygens. So 16 times 2, 32. Yeah. So we've got 68. And now what are we going to do? Divide it by 12. Okay. And what do you get when you divide by 12? Five. Okay. So 68 divided by 12, you don't get five. You get 5.6666, right? But we can't have 5.6666 carbon atoms. So we're just going down to five. So we say 5 times 12, that's going to be what? 60. So 68 minus 60 is going to be 8, right? So what do we say? Our molecular formula is probably C5H8O2, okay? And then the next thing we should be able to do is do our what? The structure. Should we do our... Well, the structure. But before that, we need to do units of unsaturation. Very good. So C5H, it should be H because it's CnH2n plus 2, right? So C5H12, right? And so we can just take away the oxygen. So C5HH8, right? And we just cancel out those oxygens. So we should have C5H12. But that gives us H4, so how many units? Two units of unsaturation. Yeah, so two units of unsaturation, okay? So what does that mean? We have two double bonds or a ring and a double bond or two rings, right? Okay. But 43, that's one of our common ions that we remember, right? What is that? Do you remember the name of it? The acyllium ion, very good, right? And that tells us oftentimes we have that methyl ketone, our methyl carbonyl group, right? The acyllium ion, okay? And the rest, 57, 57 plus 43, right? That equals 100. So from there, we should be able to just come up with something that has the mass of 57, right? You don't necessarily have to get the exact structure, but probably, well, the other oxygen is in there, right? Everybody's okay with that? Okay, so it's going to be an oxygen. And there's one, two carbons in this one, right? So we have five. How many carbons are left over? Three, one, two, three. And the units of unsaturation of this thing, remember, this comes from this. So how many units are in this structure here? One. Right? And how many are in this? Right now? Zero. And how many are we supposed to have? Two. So how many have to be in there? One. So it can be either a what or a what? Double bond or ring, right? Probably is going to be a double bond, because three-membered rings are hard to make. Okay? So probably this thing, is that fragment there? Or it could have the double bond there, but probably it's that one. And then all you do is connect these two fragments. And then lastly, you can go back and confirm to see, does that give you the same molecular formula? C, one, two, three, four, five. O, one, two, right? And two units, we should have the same molecular formula. Everybody okay with what I've done? Yep. Yeah. That's what I want you to do with every one of them, okay? And again, some of the more complex ones, you're going to have different isomers and you're like, I don't know which ice creamer it is. You can probably write either one of them will be fine, okay? Any other questions? Yeah, not today. I think that going over these three really was helpful, though, and beneficial, okay? So make sure you do the lab and that number four is a little bit tricky, so try it on your own before you ask for help.