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15. Analytical Techniques:IR, NMR, Mass Spect

1

Splitting without J-values

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So now we're gonna move on to the third important piece of information that you can get from Proton NMR, and that's going to be what we called spin split. Now, first of all, it's just important to recognize all the different terms that this could be called and how they're all the same concept. So if you ever hear of spin, spin coupling or J coupling or term I mentioned earlier called multiplicity thes, they're all the same exact concept. Okay, so spin splitting It just has to do with the concept of neighboring protons interfering with each other. And this will reveal to us the distances between different protons. Okay, Now I have to throw out a big side note here, which is that this topic can be taught either in a really simple way or a really, really complex way. And since I have no way of knowing exactly the way your professor taught it this semester, I'm going to teach it to you both ways. So I've actually made two different videos, so you can pick the easy one or pick the hard won depending on how your foster explains it. And I'm gonna help you determine which one toe watch. Okay, Obviously, if you just wanna be thorough, you can definitely watch both of them. But for right now, I'm gonna teach this topic without J values. Okay, so Jay values air the thing that complicates the spin splitting concept a lot. Okay. Now, just, you know, I've been teaching organic chemistry for a long time, and the explanation without J values, which is the simplest explanation, works for about nine out of 10 of my classrooms. Okay, So most likely you're in one of those classrooms where you don't really need to learn a rigorous explanation of J values. That being said, then this session, this one video would really just cover you for spin splitting. Now, if you're Professor goes deep into J values and starts talking about how to draw a tree diagram, that's where you're gonna wanna watch the second video. Okay. And if you suspect that you do need to learn that, go ahead and click on the second video after this one, and I'll get more into the specifics of how you know that it's important for your class. Okay, so awesome. Let's get back to the lesson. So Basically, if you're not learning J values, then this is a very simple rule. All it says is that adjacent non equivalence protons will split each other's magnetic response toe tomorrow. Okay, now there's a really simple rule that we used to predict what the's splits would look like. And that's what we call the end plus one rule. Okay, The end plus one rule just basically says that n stands for the number of So I'm just gonna write this here and is going to stand for the number of non equivalent the squib. I'm the dyslexia is coming out equivalent. Adjacent protons. Okay, So basically, and is going to be equal to this definition here. Okay. And it turns out that Pascal's triangle is actually gonna do a really good job of predicting what these different splits will look like. Okay, now, I know it might have been a really long time, might not see in Pascal's triangle since grade school, so I'm just gonna go over this really quick just to remind you, basically, Pascal's triangle is this weird kind of like mathematical revolutionary phenomenon. I don't know if that's the right way to put it where It basically is a pattern of numbers that if you add up the two numbers above Okay, then what you're gonna get is the number below. So one plus one equals two. And as you go to multiple layers, you start getting bigger and bigger sums. So we could see is that if you go down, um, you know, in one of these directions where you basically say, Well, the two numbers on the top here two plus one would equal to three or three plus three would equal to six, etcetera. So you basically take the sum of the two numbers, and that would be the number on the bottom, and then just so on and so forth. Okay, well, it turns out that these values are really good at predicting the heights of split. So this actually has to do with split heights, okay? And as n gets bigger, you're gonna get mawr splits that have varying complexity. So, for example, if you do, um, and plus one right and your end is actually equal to zero, basically meaning that you don't have any protons around that are splitting, Then we're going to call. That is a single it. That's gonna be the name of that. And you're just going to get one peak. Okay, now let's look at a more complicated example. Let's say the n in your examples actually equal to two. So that means that you have to non equivalent adjacent protons next to your target Proton. That's gonna be called a triplet. Okay. And what a triplet predicts, according to Pascal's triangle, is that since we're on the third level of the triangle, you're going to get a single split of size one a second split of size to on a third split again of size one. That's exactly what is represented right here. Noticed that I basically have a 12 one pattern. Okay, so basically, that's you can use Pascal's triangle toe model. What? Your split should look like going all the way. Just just do one more example going all the way toe like, um, a keen Tet or pen Tet. Really? Technically, it should be called a keen Tet. Um, Kinta is the better way to say it, But if you have a cane Tet notice that your peaks, you're gonna have five different splits and they're going to be of the size 14641 And that's exactly what we see here. Okay? And that is when end would equal to four. So we have four plus one, which equals five, which would be our king 10. Okay, so I hope that's making sense in terms of the shapes. Now, you just have toe actually apply it, because I know that it's still a little confusing. So let's do the first problem as a worked example Will kind of all do it together. And then the second one will have you guys do on your own. Okay, So let's go ahead and analyze this carbon right here. Okay? I'm gonna make that one my red one. And what I'm wondering, first of all, is how many adjacent non equivalent protons it has next to it. Okay. And what we find is first of all, adjacent means it's within one space. So if I go to the left, there's nothing there. If I go to the right, I do have a carbon here. Does that carbon have any protons on it? No. Okay, so it turns out that in this case, if you go to the left, there's nothing. If you go to the right, there's nothing that that means for red and is equal to zero. Okay, Now, using the n plus one rule, that means that zero plus one equals one, which means that I'm going to get a single it. I'm going to get just a single peak for the red hydrogen. Does that make sense? So far. So I would expect it just to look like a single peak. Awesome songs keep going. Now let's look at the blue. Hydrogen is over here. Now I do the same thing I say. How Maney adjacent non equivalent protons does it have next to it? Well, if I go to the left again, nothing. I'm next to a carbon with nothing. But if I go to the right Do I have any hydrogen? Actually, yes. How Maney do I have three? I have three to the right. That means that this would mean that N is equal to three. So if I use the n plus one Rule three plus one equals +44 gives me a quartet. So I would expect that I would get a quartet from those protons so those protons would be split into a quartet because I've got the three proton splitting plus one. Okay, now let's look at green. Green is over here. So if I go to the right, Nothing. If I go to the left, how many protons do I have too? So that means that for green and is equal to two. So that means according to the M Plus wannabe two plus one equals three, which would be what we call a triplet. Right? So that means that here I have a single it a quartet and a triplet. And that's what we mean by splitting that every Proton has its own unique shape based on the number of protons it's next to Okay, now, on top of that, if you wanted to predict the shapes of thes single quartets triplets easy because you could just use Pascal's triangle. So you could say that. Ah, single it. By the way, I'm not drawing these in any particular order. I'm not drawing chemical shift here. I'm just drawing shapes. The single it would look like this, right? A quartet would look like this with to 1. Actually, no, that's not what it says. That's wrong. Let's look at Pascal's triangle. Pascal's triangle actually says for quartet. That should be 1331 So I drew that all wrong. Let's do it again. So it should be one, three, three, one. And then my triplet, as we said earlier, is 1 to 1. So the triple should live like this. Okay, Now, by the way, don't worry about the heights here. I'm not. It doesn't have to be a specific height or whatever. I'm just trying to show the ratios between the different splits. Now, you know what a single it, uh, quartet and a trip it would look like based on Pascal's triangle. OK, so now we're gonna I'm gonna have you guys do be on your own and just, you know, be actually comes with one special instruction before you can solve it. Which is that it turns out that hetero atoms have a special rule. Okay, hetero atoms. You guys remember what a hetero Ademas it's important for. You know, the rest of this course hetero atoms are just non carbon atoms. That would be nitrogen, sulfur, oxygen, phosphorus, etcetera. Okay, hetero atoms. This is a big deal. Do not split. Okay, you can't split through a hetero atom. Okay, Think of it like a wall. Like, uh, wall. Okay. You can't split through it. So that means that think of this as being a complete wall, blocking off one side from the other. So when I go to analyze how many different adjacent hydrogen czar next to that well, if I go to the right, obviously there's nothing. Right? But if I go to the left, there's also nothing because I hit a wall. That wall is the hetero atom. Same thing when I go to analyze this one, when I go to the right, I'm gonna hit that wall. Okay? So just think of that. That's a special rule that I just wanted to include that you can't split through a header item. Other than that, everything else is still the same. So go ahead and try to solve for the rest of be to try to figure out how Maney splits you'd get for proton Type one proton type two and proton type three. So now the rest is up to you. Go for it.

2

Proton Splitting

3m

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All right. So, proton type one If I go to the left? Nothing. If I go to the right. Do I have any hydrogen is? Yes, I do. I have to. There. That has nothing to do with the number two just happening to hydrogen is there? So that means that n is equal to two. Meaning that two plus one equals three. Meaning that one proton type one should be a triplet. Okay, so hopefully all you guys got that. Now read gets a little more complicated. Gonna drawn arrow here to show what I'm talking about. We have to move it a little bit away. More space? Yeah, to the left. I actually have three protons. Three h to the right. I have to. Age is correct. So that means that I've got three on one side, two on the other. That means the end is actually equal toe five total right? Meaning that I have five plus one, which equals six. Okay. And six is gonna be a sextet. Okay, now, since that's one we haven't drawn yet just to show you, you could predict what a sextet would look like by Pascal's triangle. It would be a 15 10 10 51 split. So I mean, I'll quickly try to do that. It's gonna be tiny. It's gonna be tiny like this. Something like that. Okay, so we've got the tiny ones on the edges and the fives and tens. Okay, so obviously might not be perfect, but that's pretty good. Okay. And notice that Pascal's triangle helped me to know that shape, OK? And then finally, we've got on Proton type three. I'll draw another arrow for proton, type three to the right. I've got nothing. We just said, that's a wall to the left. I have to hydrogen. So that means that end is gonna be equal to two. Which means it's gonna be two plus one equals 23 which means it's gonna be a triplet. Okay, so in this case, I've got triplets, sextet, triplet. And do you guys know what this h is gonna be on the alcohol? A single it? Because I told you guys, it's n is equal to zero all the time for hetero atoms. So it's always just gonna be one peak itself. Okay, so anyway, this is Theo explanation of splitting. That is like I said gonna suffice for almost all of you out there. Okay. Now go ahead and watch the introduction to the next video just to confirm if you have to watch your not but just you guys know have confidence that if you practice this and get good at it, this probably all you're gonna need for your upcoming exam. Okay, so cool. Let's move on.

3

Problem

Predict the splitting pattern (multiplicity) for the following molecule:

A

A=singlet; B=singlet; C=doublet

B

A=singlet; B=quartet; C=triplet

C

A=singlet; B=doublet; C=triplet

D

A=singlet; B=doublet; C=quartet

4

Problem

Predict the splitting pattern (multiplicity) for the following molecule:

A

A=singlet; B=doublet; C=singlet

B

A=singlet; B=singlet; C=doublet

C

A=doublet; B=singlet; C=doublet

D

A=singlet; B=singlet; C=singlet

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