Analysis of NMR Spectra

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Analysis of NMR Spectra

Hey Ochem students, Ben Azmon here. Today. We’re gonna be doing a very last lap. We’re almost done. It’s nuclear magnetic resonance That’s right anymore. Let’s get to it I’m not gonna go too much into how it works but essentially you put a sample inside a giant magnet that’s kept really cool to make it a superconductor and then you’re going to apply a ring to it in a magnetic field and in the magnetic field you get a Spin Flint boom is spinning this way and that’s going to spin that way as far as you’re concerned the cheap way Most people are going to work out what molecule they have and verify that that’s in fact They’re doing the correct thing for us today We have our set of unknowns now, it does include IR and if you need a brushing up on IR I do have the previous video link is on the screen now and in the description down below as for the NMR itself for this Let’s start here with a chemical shift of Proton NMR of h1 NMR we’re going to talk about carpet of it later the first thing I would like you to see is like this is the quick and Dirty like this is where things will show up This is not when most of the work gets done. But as you can see something quick you can take it out so at 11:00 to even 12 you’ll see kind of a rough thing at the bottom. That’s usually a carboxylic acid if Was it called if you see a relatively sharper one into somewhere between 9 and 10 That’s usually that’s going to be an aldehyde. Those are quick and easy, of course, both of those can be verified else by IR and carbon and more you’ll see that they’re 2 then 7 to 8 is usually where all the Aromatics show up and that happens a lot. Now. There’s some more stuff to talk about aromatics a few other quick ones You can see but I won’t talk about the other things first. So we’ll get back to that next five and six we’re going to see Usually double the triple bonds also show up somewhere around here a little lower For us the triple bond age now, of course all of these this is the HS on them It’s not the C’s so it’s the H for each one that shows up Not anything else, of course, it’s wrong anymore so for an for a double bond that happens to have an H on it that will show up usually in the 5 to 6 range And then finally all the way down here. This is where all the standard CH Single bonds are within reason. Okay, usually between 0 and 3 now All of that say can be changed depending on this if you have electron withdrawing Group that is to say that it has a double bond one space away from the hydrogen From that carbon hydrogen you are interested enough this one. So it has a double bond one space away from that or That is electron withdrawing group like nitro groups Aldehydes ketones and a variety of those if you have any of those It’s going to pull your chemical shift downward and you’ll have a lower than expected if on the other hand you have a Something with a lone pair a chlorine iodine bromine fluorine some like that Oxygen nitrogen sometimes a lone pair there that that will be an electron donating group that will push to a higher to a higher than normal Chemical shift in particular you’ll also see like Something like this might show up all the way over here That’s the kind of thing that happens and this effect happens through the entire molecule With decreasing effect in each one So this one that first one here That one might be moved up a ton this one a little bit in this one just a little bit more And so there’s a little bit less so though a lot a little a little bit less and so on down the line Same thing applies to electron withdrawing And fund that you can determine where things are positioned Okay now getting into the more useful stuff. Our next topic is integration for this what essentially it is it’s the area underneath a curve and it tells you exactly How many hydrogen’s on the carbon or? whatever element That you are interested. So it’s the the hydrogen’s on that Specific carbon usually carbon. Ok, now this can be displayed in a few different ways It could be that it’s just listed on the top That’s a lot of the times was just going to be it could be that’s given to you Like is this where each you get these kind of? These kind of rows each one of these rows usually accounts for one hydrogen and so you can see here

This goes up a half and then one and a half two and a half three and so if you would expect this to be three hydrogen’s This is a older version. You don’t see it as much but it does still happen And then the last version you might see this reported as is like this This is that they just give you some random numbers here And I know from experience that Oh at this specific at this specific chemical shift I would expect this one to be a Single hydrogen and because I expect that one to be a single hydrogen I know that the base number is five and if I divide each of these by five Then I will get how many there are really so there’s three here one here and two there This happens the number is usually not quite as nice and neat this is closer to reality because in reality The computer can’t tell you specifically one But you can usually guess down to what you need it to be So that’s what you often do but for your thing, most of you are going to get something looks at this far easier to handle Especially when you’re getting started now, what what does it mean? Well, if you have an integration of one, okay, one hydrogen if it this has the reason this one it’s probably a CH And it has three of things attached to it. We don’t know what exactly but God it is ACH It could be a no HOH, but those are usually quite broad So where? where something like this might be sharp like that the NH and the O H end up being kind of fat This one is usually also taller This means to be kind of stumpy but These two, you know also for these two these can show up out of a wide variety of ranges So I didn’t include in the chemical shift, but they do happen such as be aware That’s a little less common for your problem-set the most common being it’s just a CH Then – of course ch2 now once again can be less common so theses this is each peak is How many ident chemically identical? HS there are and so for these two obviously these two are identical they can spend interchangeable You can’t tell apart. However, if you have two symmetric CHS on Tue opposite signs of molecule they can be interchange that way from the whole molecule Spinning rather than the individual bond those do show up as well. So be aware. If you see – it could technically be to see ages now so – H if it isn’t dearest – it could be – To separate see HS And 3 of course 2 3 4 is commonly if you get it It’s going to be two symmetric ch2s and uncommonly, it’s it’s actually methane This should not be in your thing, but it could happen. This is going to be a really low chemical shift So this is very unlikely, but that’s kind of fun. Not really a thing that happens 6 6 is usually two Symmetric ch3s that’s quite common. You’ll see that all the time if you think integration of six You should think that you have usually an isopropyl group that you that you might see here now I suppose you could also have three symmetric ch2s, but that’s very unlikely next up and one of the most useful is multiplicity for this what we’re actually looking at is not the Hydrogen’s that are on that peak on the specific carbon. We’re looking at the neighboring hydrogens in general the formula goes that the number of hydrogens on the neighboring peak is equal to the number of peaks minus one, so This is our spread of the few different kinds we have here the ratio of the heights We’ll talk about that in a moment the name the abbreviation how many? Hydrogen’s are on the neighbor and then some common versions of that So for us here simplest version, there’s one peak Therefore no ratio between the peaks. This is called a singlet. This is Abbreviated s of course one minus one is zero So there is no hydrogen’s on the neighboring carbon. Who knows how many hydrants are here that depends on integration This could be any one of the ones we had before but the neighbor it’s adjacent ones have no Hydrogen’s on them and for that the common versions are it’s right next to a quaternary carbon It’s right next to an alkyne Very common. It’s right next to a carbon eel, or it’s right next to some kind of atom

That doesn’t have a hydrogen on it that like an oxygen or nitrogen Even if those technically do have Hudgins if they don’t have carbons on the other side They usually don’t cause a multiplicity just because the angles aren’t quite right for that to happen Weirdnesses do occur but in general they don’t split each other. So they don’t cause this kind of weirdness happening So if there’s an O or an N, what’s on the other side? We don’t care usually Or at least it doesn’t show up. So next one two peaks. Okay ratio one to one They’re gonna be roughly the same pipe called a doublet D 2-1. There’s one hydrogen neighbor of carbon. Usually it’s a CH. Okay. Once again o H is an NHS I’m usually show up and so they won’t usually cause splitting they will they will show as a singlet as a whole if you have a CH or an NH and it doesn’t matter what’s next to it Next three peaks, okay a ratio of 1 to 2 to 1, you know, this is I think it’s Pascal’s triangle whatever That’s the kind of setup ends up happening That means that this is twice as tall as those roughly this called triplet T 3 minus 1 is 2 hydrogen’s on the neighboring. That means it’s probably going to be a ch2 technically you could still have symmetric Neighbors which each have a CH but that’s unlikely For at least for the things we’re going to give you Next we have a quartet 1 2 3 2 3 2 1 that’s 4 Peaks that means that this peak is a tall peaks are about three times taller, then the Then the the the small peak if they’re all the same height, that’s something completely different. We’ll talk about in a bit But if they have to have this ratio, okay, that’s our quartet. Okay four. Okay q is the abbreviation 1 minus 4 All these are backwards Lovely what a lovely waste of time. Okay. Now I fixed that 3 minus 1 is 2 Okay, that’s your CH 2 4 here 4 minus 1 is 3 that means this is usually a ch3 that’s pretty good sign In particular often, you’ll see these two together because you might have an alpha group. So it’s a ch2 ch2 and a ch3 Then this one’s the next interesting ones a septet But usually really tiny you need to like enlarge it to see it but I have the ratios again You can look up the triangle. I’m not gonna bother It looks triangular. This is a septet. That’s seven. There’s a lot of abbreviations the most common which is st But you’ll see a few of these. It’s usually S with something else 7 minus 1 that’s 6 those are two symmetric ch2s science to symmetric CH threes. This is a very common Isopropyl group in particular those show up next if it’s just a mess and that happens because there’s because guess what if it’s not symmetric and if you have multiple things They’re gonna lie on top of each other and you’re not going to see that for that which is called a multi-plate we call it It would put an M and as I said It can be lots of different things on this side here if I have complex splitting that’s these ones These aren’t more sophisticated things Thank you sharp bless us for you guys but I do want to tell you that it does exist and that is if you have a non-symmetric Set so there’s a neighbor on either side of you that has a hydrogen you might see that that individual woman has multiple splittings in this case if this this has two and two This is a doublet of doublets. And and so 2 minus 1 is 1 and 2 minus 1 is 1 so these are 2 CH 2 CH s which are not symmetric if they were symmetric, then they would show up over there Okay, even one of the earlier ones but if a non-symmetric they both split it in in different amounts So you get multiple splittings, of course, you can layer any number of these as you like This is a doublet of triplets DT 1 and 2. And so this is non symmetric a CH and a CH 2 Obviously those company signature all this is the main things that you used I’m going to show you how to use in just a moment. The last thing you should know is in general They will slope up to What is causing them to split? So in this case? This is sloping up to the right. So we would expect the thing that split it to be on its right same thing here That’s up to the right here. You can see that again that’s up to the right these for a For septet it’s a little harder to see but once again it is these ones that you care about Multiplets you can’t really see and for here for a doublet of doublet

You can see that this one slopes up to there and that one slips up there because they’re splitting Each other and the same thing here. This should be like that Technically I thought to that because they are splitting each other so up and towards each other Okay, one more word here about aromatics for these ones. There’s four main ones that you’ll see for this kind of thing And they have specific integration like the pattern you’ll see and what they actually look like and then what they’re called So if we have an integration of five in of course, this is for aromatics So this is between chemical shifts 7 & 8 if we have an integration of 5 And it’s a mess. It’s a it’s a multiplet. You don’t even want to touch it. It’s ugly But it has five inches in that region. You’re looking at a phenyl group Okay, you have one connection to the aromatic ring and the rest are hydrogen’s and they overlap each other now Sometimes you can distinguish a little bit depending on what other groups you have here but in general if it has five stings regardless of how Complicated a simple. It looks it’s probably phenyl group. That’s four. We have three different options here. So For us if we have the nice clean doublet of doublet. That’s real easy That is just going to be a para position right here. So they’re opposite each other and the reason what you’ll see here is sometimes you’ll see this as an integration of Four for everything or you might see it as two inches and two H’s either way pair up these are opposite each other next if you see an integration of a singlet and a multiplet usually That and this here and you’ll either see this integrated as four or as one Here one hydrogen there and three hydrogen’s there that is going to be meta there are one Three to each other one two three, so there’s three hydrogens here and then one by themself This one is almost always going to be higher just because it has those extra pieces right there That separate it. So of course, these are other connections that are not hydrogen. That’s what that the that’s meant to symbolize so here this guy’s usually higher up as you see either three or one was four with this pattern and Four here if you see a multi an integration of four, and it’s Wholly unreadable usually two low-end That some kind of multiplet that is as a whole going to be the ortho 1/2 to each other that those four hydrogens all on the same side now switching over to carbon 13 NMR We have a few things to discuss here First is that it’s basically all chemical shift. There is no multiplicity there is no integration and but mostly It’s essentially all chemical shift and you can in general figure out exactly How many carbons you have just like technically you can figure out how many hydrogens by literally Counting that total integration you can figure out how many carbons you have by counting how many Peaks you have but these are of course these are unique Carbons, so if you have symmetric, they will show up in the same spot So they’ll be 1 2 3 4 6 7 8 9 10 11 12 For our kind of a nonsense thing here Ignoring of course this this is the only kind of splitting you’ll ever see. This is usually happens at 77 This is just a solvent. It’s a triplet looking thing don’t It’s it’s it’s just ignore it if you see it But in general you have these and mostly they’re all the same height With the exception of if you have a symmetric Something they may in fact be twice as tall If you have two of them three times tall if you have three of them which are symmetric This isn’t a perfect thing you’re kind of like waffling because sometimes it’s gonna be in the middle and it’s gonna be like is this really is it not so That might indicate that you always put as an asterisk. So that might mean that there’s a symmetric set here or might not and And then for these guys are really late ones. Those are always tiny So those are quaternary carbons in particular from above 202 and 220. Those are aldehydes and ketones And then 160 to 190 ish is where you have carbon click acid esters em It’s acyl chlorides variety of other things. And those are all of course those tiny little things to see much of them next is in the big bulk here from about 100 to 160 is where double bonds show up as well as Aromatics, of course our men have double bonded and so that’s what you’ll see in particular I have here two examples of aromatics for an aromatic ring

Regardless of what’s on it you almost always assume means there’s anything on it Like if it has one group, then you’ll have it or more of this pattern If it’s there’s no groups in it’s just one line But if you have at least one group You’ll usually see two of them tall in two of them short in this case You see the order it doesn’t matter so it could be tall tall short short or tall Short tall tall or short whatever word it doesn’t really matter, but for an air bag thing You see tube tall too short because you always have these two will be symmetric So they will show up together and these two will be submitted. They’ll show up together And then these this will be independent that will be independent and so they might show up like this or that and that depends on as before electron withdrawing and donating groups left on withdrawing groups Lower your ppm electrons the that’s a unit here the electron donating groups raise that You have a higher chemical shift in general So if you have an electron donating group here You would expect this one to be higher and you’d expect those two to be higher in a variety Then the ones next one because of course it transfers multiple steps down as well each time a little less Last couple here is over here We have triple bonds which are rare but do you you’ll see them in the 70 to 90 s range and then every other kind of single bond to thing is From 20 ish to 60 70 ish? You don’t really see that low, because of course Below 14 ish 12 ish? that’s where hydrogen in the more so you’re not going to see that in carbon in mark the next part of carbon and Ammar is these two additional kinds of tests that called depth 90 and depth 135 there is a ton more in Tamar as you can do but as far as you’re concerned these are the main ones now what how they differ from regular carbon is a regular carbon will show see quaternary CHS, so aldehydes ketones are just something that has four so CH s CH 2 s CH 3 So I quit her name C’s not CHS, of course. There’s no H there. It can’t be done at the Cutrona They will show them and I’ll show everything up. Okay, it’s just like this. They’re all facing up just like you would expect them to however for carbon and for depth 90, okay, depth 90 You don’t seek returners. They just manage So that means that this one here and that one there were quick to most likely return Aries We expected this one to be quaternary. Anyways, just because of its position but That that would tell you that’s most likely equal ternary However, you’ll see there’s a few other missing piece the other things are missing our CH 2 s and ch3s only CH s appear for at depth 90 so that 90 only gets CHS and no ch2s no c CH threes and no pattern Ares. So you see the theory these are gone too and then Foot depth 135 again. No coronaries but this time we do have the CH ch2 ch3 but CH and ch3 Are both going to be facing up or weirdly enough? Ch2s are facing down. So using all this pieces of information. You can figure out what something is So if it’s only missing from 135, then that means it’s a quaternary That means that that one is a quaternary and this one is a Quinn ternary if it is missing from if it’s down in the 135 then that’s definitely a ch2 no question about it if it’s present and up in the sea in the 135 but absent from the 90, that should be Ch3, which means everything that’s left here. That’s only in the 19th. OHS are all CH s That tells you a lot about a molecule that allows you to figure it out now How do you apply all this into one thing? Okay. So this is one of my favorite examples to do this involves all of this data okay for our Compound and they’re all the same compound. This is the type of thing. You might see For us here, of course This is our IR this is our H NMR and this is our c-13 NMR Now starting with the IR quick brief things we see two peaks somewhere Below 3000 that means we’re probably here looking at CHS. Okay, we There’s some kind of single bonded okay now that could be

CH ch2 ch3 regardless what it is. It’s single bonded. That’s the important thing Because it’s not high enough to be double bonded and then we see another one 1750 that is some kind of carbonyl Okay, so we know that we probably have some kind of crab meal and then there’s some mess down here. That’s pretty low We don’t pay attention to it. That’s part of the fingerprint region for our hydrogen atom are already quickly looking at it We can see we have 1 2 3 4 5 6 7 8 9 10 11 12 We’re going to have 12 hydrogen’s total for our thing. So we expect that our formula Will be something in the ways of H 12 and for the carbon we see 1 2 3 4 5 carbons so that Probably is 5 but that’s not guaranteed Remember that can’t have symmetric. We don’t know for these guys here are symmetric or not So this is five, maybe okay, we will see about that if that makes sense for it to be five Now back to the hydrogen anymore now what we would like to see for something like this is I like to make a table like this. This table is just a manifestation of how a chemist thinks about it It’s easy for you to use when you’re starting on later on you do most of this in your head But for this for our first peak and I label the peaks ABCDF or Peaks I find it easier to talk about in to think about if I have a label for them So for a we know how many carbonate hydrogens are on it, or we have one that’s easy enough for B We have two it is literally given some just copying it down for four. See it’s 6 and for D It’s 3 that’s easy enough And as we said before, what is this most likely well, most likely this is going to be a CH of some kind. Okay? And this is a proper CH it’s not just any single bonded. This one is going to be most likely a ch2 And this 6 remember, can you guess where this? Yep? That’s 2 CH 3 s 2 symmetric CH threes and then here once again, we see another ch3 That’s remember this is integration integration Is part of what is actually on that peak? It’s that one then looking at this quickly for multiplicity. Okay, that’s what all of these are. There’s a multiplicity multiplicity for the first one here We have 1 2 3 4 5 6 7 piece it even says there set that so that’s seven peaks That means that the hydrogen’s should be one less than that. That means 6 hydrogen’s on the neighbor Here because it’s always minus 1 regardless of what it is. It’s always minus 1 so that makes this easier to interpret Then for B, that’s a quartet. That’s one two three four. So that means we have three Hydrogens on the neighbor remember all this is the neighbor and then here too so that means we should have one hydrogen on this neighbor and Here’s the triplet. So a triplet is three That means this should be two hutchins on the neighbor what this means for us here is most likely what this is this for this one six just like before that’s 2 CH 3 s 2 CH 3 s and Here for three. That’s a ch3 and here for one That’s a CH a proper CH. It’s not just single bonded And then this is a ch2 because we have two here So for this we can already see a pattern emerging and that first pattern is that this is a CH that sees a Ch2 ch3 s and this is 2 CH 3 s Let’s see the CH that means that a and C should be next to each other and I’m going to put C on the outside because those are terminal so what that might look like for us is Something like this. Here’s our Ch3, here’s our ch3 and we are connected here to our CH Which has one more connections three connections here we need to make one more connection what else do we see well, we see over here we See over here well This is a ch2 that sees a ch3 And this is a ch3 that sees a ch2 these two are probably paired up

And so what we would expect is we’d have D and B together Once again, I’m putting D on the outside because it’s a terminal so that would make it for us here That our D Ch3, is there connected to a ch2 with one more connection between them now that already has one two three four five carbons okay now For this I Did make a little weirdness here. So for our carbon, I made a little correction here This one is in fact twice as tall as it should be Because we do have so much but you of course won’t be doing Corrections. I’m just working with this quickly off the fly, but We can see here that we actually it could have been five But it could have also been six if that was a double even if you didn’t see that That like even if you I made it nice and clear now but it’s not guarantee that you’re gonna see it every time that’s why I put a question mark So at the moment, it looks like there should be something else here because we know we have a carbonyl carbon eel wouldn’t show up? Here especially unless it was a carboxylic acid We don’t have anything to be carpet silic acid or an aldehyde does the other ones a carbon eel? So it’s not that so it has to be some other kind of carbonyl so that carbon in we can see here We also have something that looks like a carbon eel That’s not an aldehyde or a ketone Okay So that means that this is most likely an ester. So that’s That that’s what we’re gonna go with here and we’re gonna go with this here is probably an ester of some kind So we need to have connections on either side now Just to confirm from all of this we can see that we can see here that From our information we have five here. These are all kind of single bonded things That’s most likely a carbon eel, and over here from the depth information. We can see that okay, these are both gone So that’s definitely a coronary so that doesn’t surprise us So we re expecting a carbon eel Most likely an ester because a position is not is too low to be an aldehyde or ketone so ester is the most likely Then But of course these can be other things you do want to look at your problem given or Sometimes you’re given Additional information that will say on this definitely necessary not amador some like that I’m gonna say it’s an ester because I made up the problem and I know that it is for us here 50 so here is present in in F 90 and it’s up in depth 90. Okay. That means that In depth 135 that means if it’s present there that must be a CH Okay, there’s there’s no other option here. These are all absent and these two are up So these have to be ch3s, okay So for this one over here for these two we can see that the DEP nominee is absent But they’re both up that guarantees of these as suppose. We CH threes that’s these ones here and that this one here Was a call this one in the middle because it’s down for death 135, that should be a ch2. Yep, I wrote three Should be a ch2 Now that should tell us already Most likely where these are going to be now for for us we know that we can have an ester and we know that we have these so For our compound when we label them those that I labeled here We need to kind of figure out how to put in our ester and then we’ll label these in a moment But they all line up with what we already expect So our ester we have two options are two options is we can either put it this way or we could put it this way So we can put it either way when you kind of have to figure out which one is better for us and For this because if we put it in that way This one will be closer to electron-withdrawing this one close to like I’m donating We would expect this to behind not to be low for putting the other way around This is next dude withdrawing so it below this. The next is donating you said behind so are that whatever ones are highest one should give us away and for us a is In fact, our first one that is this one so we would expect this to be a in this order here To actually solve our molecule. So that’s our molecule for this and so we can get rid of that We don’t need this anymore. This is our molecule as we anticipated Our last thing we also have to do is we have to redraw this molecule one more time

ch3 ch2 Oh See, oh see H and then ch3 and Then we want to label These with also with some kind of labeling scheme Now if your paper gives you a specific little scheme to follow label as they say in the paper If it doesn’t choose whatever labeling scheme you want I’m going to use lower cases in this particular case a B C and E And so of course, this is a B C D and E now For us here, we can already figure out. Okay. Well, this is the ester. That’s the a that’s nice and easy This ch2. Okay. That’s C. That’s nice and easy then 22 here and then 22 here is twice as tall and So we would expect that to be these guys over here. So that’s 22, which we call D that means these two are going to be d and between these we said that this is a ch3 and that’s a CH so our CH has to be B, and this has to be Our remaining one here, which is a B C D and E so that’s e that’s also the other way we can figure this out is We know that The closer you are tor grew to the main group the center. You should have a higher Proportion so between these two You would expect that this which these two CH threes that we want distinguish Between Dean’s and E That this one which is closer to an electron donating group should be higher up than this one which is closer to electron withdrawing group and we see that here that between these two CH 3 s D is higher up than the E. And therefore this two should be D and this should be e You want to fill all this out in your form? So these are the hydrogen assignments with each unique hydrogen and these are the carbon assignments make sure you also give me if this is a Ch2 CH C so through what is it? What group is as an ester or whatever? That’s it. You’re done