 Okay, so let's try this example A that says unknown sample of hydrocarbon with only one oxygen, C-X-H-Y-O. So I guess the first thing that these questions oftentimes ask is where are those two main peaks, the base peak and the parent ion? So let's go ahead and ask those particular questions. Where's the parent ion? 134. 134. How do you know it's that one and not any of the peaks, the other peaks? Yeah, so the highest mass, okay? Oftentimes there's a tiny little peak right after 134 or right after this parent ion. That's the M++1 peak, don't worry about it, okay? That's because every once in a while there's a carbon 13 in one of the molecules that it's looking at. The other thing we notice here that the molecular formula they give us, or at least part of it, C, H, and O, right? If we have only atoms that are C, H, and O, the compound has to have a what type of mass? An even number of mass, right? It's only gonna have an odd number if it has a nitrogen in it. So that gives you another clue as to, oh yeah, that's the parent ion, okay? In fact, if I look at all the other ones, they're all off, right? So you can logically think this stuff out, okay? So let's go through some of these peaks. Oh, where's the base peak? 91. 91. How do you know that's the base peak? Follist, biggest, whatever you wanna say, okay? And 91, is that a common ion that we usually see? Are often times C in these things? Yeah, what ion is it? Okay, it's a benzyl group that does what? Rearranges, yes. I know we wanna say it's a benzyl group, but it's actually a what ion? Billium ion, yes. So it's that thing. So like you said, it came from a benzyl group though, right? So we know that we must have a benzyl group in this molecule. That gives us a clue, the structural information, structural clue to this molecule. Here's another clue to what's in this molecule. When I look at this peak here, right? I can tell what it probably is by looking at the difference there, right? So what's the difference between 134 and 119? 15. 15, so we subtracted 15 from that to get 119. What's a common group that you guys know that's 15? Look at your common groups. Metcal group. Metcal group, right? So we think, okay, there must be a methyl group there. Everybody okay with that? Okay. Then the other thing we can, well we need to know what its molecular formula is, right? So 134, and we know there's only one oxygen in there, so we can already subtract 16, right? So 134 minus 16, and that's gonna give us 118. Okay, and then from there we should be able to decide how many carbons and hydrogens there are, right? So how do we go about doing that? We take 118 and divide it by what? 12, and that gives me 9.8. So does that mean I have 9.8 carbons in this thing? No, that doesn't even make sense, right? So what would be a good number to start with? Nine maybe, right? So we'll say nine times 12, that equals 108. And then that would mean we have 10 hydrogens, right? 10 hydrogens. Okay, does that seem reasonable? Yeah, that seems kind of reasonable, right? So C9HN, is that what we said? Okay, so let's see how many units we have in saturation this is going to have. Okay, so it should be what? CNH2N plus two, so that's C9H20. So how many units? So if we take C9H20, subtract C9H10, we get H10. So how many units? Five units. We know it's already got a what in it? A benzene ring, right? A benzene or benzene group, which contains a benzene ring in it, right? So how many units of in saturation does that benzene ring already have it? Three plus one, because it's a ring, so it's four, right? So we're only missing the one unit of in saturation. Is everybody okay with that? Okay, so this 43 here, okay, this 43 here, that's a common ion we've been seeing as well, right? The acyllium ion, you guys remember that from the table? So the acyllium ion is that thing there, okay? That comes from having the methyl carbonyl, okay? So that was derived something like this, okay? In fact, those are just resonance structures of each other. And then this one, what did we say, came from the benzene group, right? Like that, okay? So one, two, three, four, five, six, seven, eight, nine. Four, five, six, seven, eight, nine, okay? So we put those two fragments together, and guess what? Guess, guys, think you're good? You're gonna guess? What do we guess? The molecule, that's the molecule.