 Okay, so since we've been talking about this mass spec stuff, here's an example of an alkyl halide. So it says an unknown sample of an alkyl halide, CXHYX, where X can equal either chlorine, bromine, or iodine. Right, and it's showing us this mass spectrum here. When we look at this mass spectrum, how do we identify which halogen we have in the spectrum, or in the molecule? Well we have to look at the parent ion. Yeah, when we look at the parent ion here, and we see it's the ratio of them is what? One to one. It's one to one, right? Yeah, very good. You guys are doing great. So when we see that one to one, that gives us a really big clue as to which one of these halogens we have in it. So which one is it? Bromine. Bromine. Very good, guys. So bromine, there. And why do we see the two parent peaks with the bromine? Yeah, so there's two isotopes of bromine. Okay, so that's something you've got to remember. So when we look at the periodic table up there, and it says the atomic weight of bromine is 79.90, we have to remember that's the average atomic weight, okay? That's not the atomic weight of every single bromine atom. So the two main isotopes of bromine are actually at 79, almost exactly, and 81, okay? And if you look at the average atomic weight mass, that's almost at 80, okay? So you can kind of say, well, they're at a one to one ratio because they're effectively 50-50% of the population. That's why we see that one to one ratio. So that was that question that we were having trouble with earlier. Okay, so let's see. The other thing we know is that we have... So if we subtract that number, 79 from 170, what do we get? 91. 91 right here, okay? So remember I told you, always keep in mind those particular fragments that oftentimes come up, okay? That 91 is actually a very common fragment, so let's go back to that common fragment. And when we look at these two different sides of the table, this is commonly lost fragments, and this is common stable ions, right? So which side of the table left or right is the mass spec actually detecting? The right. The right because they're the ions, right? The positively charged. That's what the detector detects. So when we see a line in that mass spectrum, that means it's detecting it. So remember that big peak or the base peak, right? Was that 91? Okay, this is a very common ion. This is what we imagine it to be the tropillium ion. But that comes from a benzene group, okay? And of course if we add 91 to 79, we get 170 here, and if we add 91 to 81, right, we get 172, okay? So the structure for this molecule is almost certainly the benzene group with a bromine attached to it, or benzene bromine. Is everybody okay with that? Yes. Okay, so that's the way I want you to go through these things. And like I said, this mass spectrum is not the best way to come up with structural information for all the spectroscopic techniques that you can do, okay? So there's this other one called NMR which you haven't learned yet that's going to give you much more material to work with in determining the structure, okay? So the mass spectrum is kind of a way to identify portions of the molecule, but mostly it identifies what the actual mass of the molecule is. But in ones like this, you can see, oh, that definitely has a bromine. Is everybody okay with what I'm saying? Yes. Okay, cool. Sorry about the glare there. Oh, one other thing, let's just identify the parent in the base peak here, okay? We've mentioned them already, but if I say in, like in a question, what's the base peak? What would you say? Ninety-one. Ninety-one. And why is this one the base peak? It's the tallest peak. Yeah, it's the highest peak or the tallest peak is always the base peak, okay? Yeah. And then the parent ion is what? It's, yeah, 170 and 172, okay? So normally we don't have two parent ions. And then if it asks you, draw a structure for the fragment, the tropillium ion. So that's the benzalion rearrangement. Does a rearrangement, because that's actually the worst thing. Any questions now? No. Okay.