So guys, mass spec is an analytical technique that's used to weigh your sample. So you place a sample unknown molecule through a mass spectrometer. Mass spectrometer and it should tell you the weight of your moloch. Okay, now, the way this is accomplished usually is through a process called electron impact ionization. Or simply E I. Okay, this is the most common form of mass spec and it has to do with electrons hitting your sample at a very, very high speed. So guys here, I have the general scheme of how a mass spectrum works like the actual equipment and what you do is you have your unknown sample. So in this case you can tell that my sample is methane. I know it because I happen to draw it, but if I was out in the field, I might not know what the sample is. So I'm processing through my mass spectrometer. And what's gonna happen is it's gonna go through a series of steps whereby at the end, I can actually tell what its molecular weight is. So let's go ahead and follow the bullet points. I'm going to go over how this machine works. So the first thing that happens is that electrons are going to be beamed at these molecules. Remember that? I said that this is called electron impact ionization. So you're gonna be shooting very high energy electrons at their molecule. And what this is gonna do is it's going to generate a high energy intermediate called a radical cat iron. So where is this happening? We're looking at my diagram, This would happen right at the ionization phase. Okay, so your sample is actually first vaporized. It's turned into a gas that's over here. So you're putting a gas through your mass spectrometer and then we're ionizing it. We're shooting these very fast single beam of electrons at the molecules and trying to break them apart essentially. Okay, so when you break it apart, you're gonna get something called the molecular ion. Okay, now, what a molecular ion is is it's your same exact molecule but it's with one thing missing and what it is is that it's your molecule missing one electron. Let me show you how this works. Imagine that this carbon initially has eight octave electrons. Right? Remember that every second row element most of them want to have eight electrons to fulfill their octet. Well, after I shoot these high energy electrons at my molecule, what's gonna happen is that one of them is gonna get dislodged. That's what I'm counting on. I'm counting that one of these eight electrons is gonna go missing. It's gonna just bounce off and what's going to happen at the end is that we get this thing called the radical cat iron. So you can see is that the radical cat iron is the same thing as before. It's the same molecule. But instead of having two electrons for this bond, I only have one. Okay, so imagine that basically that electron is now one of them is missing. So that is what a radical cast iron is called. That's how it's made and the reason it's called a radical cat iron is because first of all it has a radical now, it just has one electron between those atoms instead of two. But also the entire molecule has a positive charge. Because as you can see we're missing an electron. So that means one of these one basically this entire molecule is going to have a net charge now. Okay, so the way we symbolize in short a molecular ion is we write capital M and then we write a positive and we write a radical and this is the same way to say that it's a radical cast iron because it has both positive character and it has a radical. You may also see in your textbook or in your homework that it's abbreviated as M plus radical to the side. It's the same thing. It's just a different way to draw it. But I like to draw them up and down. Takes less space. Alright, this is also by the way, it's also called the parent ion. So if you hear a parent ion, if you hear molecular ion, if you hear a radical cat eye on these are all the same exact things, you need to know your terminology. Alright guys. So now we've ionized my sample, right? That's the ionization phase. What happens to the rest? You can see that there's other stages. It says deflection detection, there's a magnet. What's going on. Well guys, it turns out that only some of these fragments are going to be magnetically sensitive. Okay. And it's the ones that are charged. So it turns out that fragment cat ions, okay. Whenever you get a cast iron produced by the ionization of this molecule that's going to be deflected by the magnetic field, but not all cat ions are alike. It turns out that smaller ones are affected more than bigger ones. So that means that this is just due to physics due to inertia. Imagine a small ion if it's moving through the tube, it's much easier to deflect it because it has very little inertia. Whereas a large ion, if it's very very big, it's gonna be more difficult to change its path. It's gonna be more difficult to accelerate it and to deflect it. Okay, so what this does is it gives us the ability to detect where these radicals are, sorry, where these cast irons are hitting. If it doesn't deflect very much. I know it's really big and heavy if it deflects a lot then I know, okay, this thing is small and that's exactly what happens here, it passes through a magnet where it gets deflected and I detect how much did it get deflected and through this I'm able to determine helping the masses. So what we actually get as a reading for a mass spectrometer is not exactly mass but it's close what it's called is the mass to charge ratio where your mass is equal to M that's an ugly M let's do this again. Your mass is equal to M and your charge is equal to Z. Okay, now we just stated what kinds of charges are sensitive to the electro magnet positive charges. Okay. Cat irons. So what that means is that even though we're detecting the mass to charge ratio, MZ? Really, Z is usually going to be equal to one. Right? Because we said that the ones that are sensitive and getting detected are the cat ions. So that means that even though you're detecting mass over charge with this really equals is mass over one because the charge is always one and any number over one is just itself. So what that means is that really this is just a fancy way to determine the molecular weight of your catatonic fragments, the ones that are positively charged. Is that making sense so far? So now we've got the mass of your fragment. Okay, now we just have to learn in terms of finishing this page. How are we going to read a mass spectrum if we're given one. So guys here is the mass spectrum of our molecule. Okay, this is what we would actually get in the reading And what we would see is that the radical cat iron here, remember that the radical cat iron only had an electron missing. So the radical cat iron is going to have the weight of the initial sample. Okay, so remember that the formula for this is CH- four. And if you were to approximate the weight in the weight of this molecule, carbon is equal to 12. And your fours are I'm sorry and your H is age four is equal to four. So you should get 16. Okay. And that's exactly what my mass spectrum says. It says that the largest peak, the largest peak, the base peak is my radical cat iron. Now maybe wondering johnny, how can it have the same weight as it did originally if you knocked away an electron? But keep in mind guys that electrons don't really count towards molecular weight because they're so tiny. They have such little mass that you can afford to knock it off and your molecules basically gonna have the same mass. Okay, so really what we're doing is we're just measuring the weight of our radical cat in here. This is what we would call our molecular ions that B M plus radical. Okay, but now we see that there's these other peaks on our mass spectrum as well. There's one at 15. There's a smaller one at 14. What's going on there? Well guys, these would be basically fragments these would be catatonic fragments that formed because this molecules hit with very high energy electrons. So sometimes it's just gonna knock off an electron and that's all that happens. But sometimes it's gonna bust the molecule open. So the 15 would be what we call our m minus one because it's our molecular ion minus one. But why is it minus one? Well, that would be losing a hydrogen. That would be if I actually knocked off an entire hydrogen instead of just knocking off an electron, I would get 15. Okay. And what you can see is that is this a common fragment? Absolutely notice that my M minus one peak is almost as tall as my cada as my molecular ion. Why is that? Well, because it's very easy for methane to knock off one hydrogen. Okay, but you can see that the more hydrogen chip to knock off, the less probable it is to get these signals. And that's exactly what happens. So 14. That would be that would be that I'm knocking off two hydrogen. Right, this would be my M minus two. It's much more difficult to get that because you can see that the number is far far lower. So just kind of makes common sense that the more atoms you have to knock off of this fragment, the less likely you're gonna get it, the less, you know, you're going to detect it in your mass spectrum. Okay, now, I just want to point out a few other things about how the axes work here, the X axis is easy mass to charge. You guys already know that that really just stands for mass. Right, But I haven't talked about the Y axis yet, which is the relative abundance. We're saying that there's 85% of 100% of another. What does that mean? Well guys, it doesn't mean, for example, it doesn't mean that 85% of your notice that I have an 85 next to 15 guys. That does not mean that 85% of the hole is made out of your n minus one. Well, all it means is that compared to your tallest peak, Which my tallest peak here happens to be my radical cat iron right happens to be the molecular ion compared to the tallest peak, which is the 100. I have 85% of my minus one. So essentially all this is saying is that if at the end of the day, I run my whole spectrum and I get 100 of these molecules, I should expect to find 85 of these. Okay, so it's just 85% as likely as the base peak. Okay, now that comes to another term, I keep using this term base peak

So the base peak of the sample is simply going to be the tallest peak out of all of them. And we always scale the base peak to be 100. So that means that we make our base peak 100 then we compare everything else to that. Okay, Now, in this case, my base peak happened to be my molecular ion, right? The M plus radical. Okay, but this isn't always the case. Later on, when we talk about fragmentation, what we'll see is that sometimes the base peak is actually gonna be one of the fragments, because sometimes the fragments are more stable than the molecular ion themselves. So in this case, I gave you a simple situation where the base peak is actually equal to the molecular ion. But we're going to see later on is that sometimes one of the smaller fragments is actually your base peak, and your molecular ion is lower because it's more common than fragments than that it doesn't does that making sense. Awesome, guys. So this is just an intro. Now, what we're gonna do is we're gonna go more into fragmentation patterns, and we're gonna talk about isotopes okay, By the way, I want to point out one thing, which is that notice that there is a tiny peak at 17 that I didn't talk about. That's how did that happen? Doesn't mean it has one extra hydrogen will get there. Okay, that's its own kind of it's phenomenon. But for right now, just focus on 16 and below, because that's what we can understand through the process of ionization. All right, so let's move on to the next video.