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Lecture 19. NMR Spectroscopy, Part 3.

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it's been a lot of buzz in the media recently about 3 D printing but not all of it good but most of the good guys talking about the possibilities is this idea that may be some gave a piece of your microwave oven breaks you don't have to send it away just make some new little part in your bedroom and install yourself for it the heel off your shoes breaks you just print out a new appeal to your shoe include on in and you're good to go on so they could talk of
just a tiny tiny bit about this idea of 3 D printing from that you can have these these devices in the Pacific pregnant controllers had always do this if I can pull this off on there may not be
possible you can watch a 3
D printer action Bloomberg and what I about to the trip but the
society know about them more and it is the but in the sound is inconsequential but the main idea here is that if you look at that you can print not pieces of paper like I write my lectures on the actual 3 D objects and as long as you can imagine each plane of this object is being what you draw on a sheet of paper you're perfectly capable of printing out complex machine parts anything you need why go to the store anymore to buy things you can just download the instructions instead print things for yourself and it's amazing the complex objects that you can make this is coming to health care through business near you in fact it's already there they print out 3 D models of teeth of skulls on little pieces that you can put in the ear plant in the human body on a number of those types of three-dimensional printers servers anything the school of course has to involve organic chemistry and has come back to that Of course but what is
this treaty printing business
here I'm going to show you the lowest tech possible there many varieties of ways to deposit three-dimensional materials and they're not all organic you can also do this with medals amazingly I'm going to show the cheapest version there just now dipping below a thousand dollars to buy up to buy and have your own three-dimensional printer of the fanciest ones actually create new molecules at the at the site of the printed them little or little lasers that point down and create new molecules doing photo chemistry but the lawless Technomic the kind that you're likely to buy 1st but in the near future actually use the spools of plastic and all they do is feasible plastic along lines you cannot have different color 3 D printers to pretty amazing objects of the feasible spools of plastic thread and then right there at the printed they melt them and then deposit them on a three-dimensional surface and sometimes they have an extra line with filler in there in cases overhang so that you can pretty easily distillate can be easily washed away when you're done so that you leave gaps where that filler used to be so there's still common plastics that are used in in those cheap fillers for the cheap style 3 D printers that you're likely to end up with in your home and this is 1 of them polylactic acid on and I think the other 1 is based on an acrylic acid resin we were not going to talk about that and this is polylactic acid it's a very and based on a very simple monomer lactic acid it's something that you have in the human body and it's also a molecule it's considered a biopolymer that you can get from bacteria on a renewable basis so that we haven't talked about it at all about polymer chemistry but it's this repeating unit very similar to 2 of the amino acid alanine so if you replace that with an NH this would be basically a polymer about winning but naturally occurring polymer are that you can find in nature it's a Apollo it's a polymer that took lends itself very well to this process of melting and depositing so I'm I'm guessing in a few years some of you guys are going to have these things in Europe in your home in your bedroom or office printing out objects may be printing out of medical devices or not out of this material so take here take what you learn in this class and go designed some new classes of of biocompatible plastics and you can print out new parts for my human bodies it degrades over the next 10 years and so I need you to work on that realistic returned back to about 2 and a mock me appointed the sapling homework right were not finishing the day Panama's section Chapter 14 until today some extending the hope the sapling work for Chapter 14 until Wednesday but until Wednesday evening at work covering probably today the most of most complex part of animus but trust baby and it's called splitting so I mentioned yes sure sides and somebody has to turn the volume up the move Jeremiah the negatives just talk louder freedom and was running I'm right on the edge here feedback so that's good for the soul of world where on the last part of spectroscopy and I mentioned that there 3 different things that affect the frequency which protons resonate in the proton NMR spectrum and the single biggest affected you will see in a proton animosity that from that shifts things is magnetic and I Satrapi protons that are directly attached to carbons that a part of CC double-blind in benzene rings the circulating currently gets generated in a benzene ring creates this tiny little magnetic field and the closer I am to a pie bond on benzene ring the 1 going to be shifted downfield to 7 and 8 parts per million so magnetic that I cited is the biggest effect in Proton marked the 2nd biggest effect and proton and Mark is being next to a lecturer negative Adams it's this D shielding effect that I'm next to some chlorine fluorine oxygen it will suck electrons from away from me so I can see more of the magnetic field so that's the 2nd biggest effect and then the last effect were going to talk about today and that is the effect of nearby protons every little Proton is a tiny magnets and because every little Proton is a tiny magnets I'll be able to see those protons other nearby me because they either lead to a bigger magnetic field or a smaller 1 OK so it's let's take an example of Of this effectively Internet site let me turn it down a case of proton neighbors couple and so it's going to think about this bold Proton here and neglect and tried to circle it with a different color or just underlines McKinsey where attention should be focused this is going to create huge problems for you that you're always I'm going to it can very easily get confusing about which protons were trying to focus on so let's focus on this boxed bold Proton there and consider the effects of the neighboring protons were interested in the wreck the resonance frequency of the box Proton there it's gonna neighbor uses neighbor and what I'm showing you is that this Proton has to quantise choices it's either spin or spin down about 50 per cent of the molecules are speeding up about 50 per cent of the molecules the spin down there is a slight population difference if I take 6 . 0 2 times 10 to 20 3rd molecules on average 50 per cent of that mole of protons or molecules love this Proton with spin up and the other 50 per cent of the Of those molecules with this Proton with spin down so in other words this Proton for half of the molecules this Proton will feel a slightly bigger magnetic field and then from molecules like this this Proton will feel a slightly smaller magnetic field because this magnetic field here as tiny as it is will subtract from the online magnetic field so that you don't see just 1 peak you see 2 peaks the boxed red Proton will exist is to peaks because it has 2 different types of neighbors and so the important point to remember is that Adam Arkin never we it's not sensitive enough to look at 1 molecule we're looking at populations of zillions of molecules at the same time so wishes remember that these 2 protons and will have different chemical shift because of that neighboring protons now why wasn't this approach the problem with carbon animal we we never had any splitting problem of carbon and marked would draw a typical 1 at a section of a large lacks molecule for you just this is just meant to be some run-of-the-mill organic molecule with lots of carbon atoms in the backbone doesn't matter if the rain doesn't matter if the branching here the point is that if I take a look at a typical carbon molecule most of the carbons are carbon 12 that have no spins carbon 12 carbon 12 it's the carbon 12 isotope that's the 1 that's common 99 out of 100 carbons are carbon 12 it's only 1 out of 100 and only 1 out of 100 cartons will be a carbon 13 and so the chances that this carbon 13 is going to be next to another carbon 13 is so small there's almost no chance that the every bit if you grabbed a carbon 13 it would have a neighbor that's also a carbon 13 so in this very little chance that you'll see on soldiers right here no 13 C neighbor on average that's was day on average with typical Circle see 30 molecules will not have another carbon 13 neighbors that just doesn't happen so we never had to worry about this splitting up that with carbon 13 animus that trust be on that was never an issue for us so what a wonderful situation for carbon and now Panama and that's why I started with carbon and a mark it makes the interpretation of this of the spectra very simple focus would go back to this proton NMR business because it makes so it will make our lives of substantially more complex and we have to deal with that OK so it's good and talk about what happens it if we have 2 different populations of molecules what I want to do is I want to sketch out a tiny little spectrum up on top here and below that of draw these 2 possible
situations 4 of a molecule with the Proton has enabled so many the same molecule twice so here all draw a molecule and we're really interested in this Proton it's next to a chlorine atoms just as it gives us something to focus on and here it's got neighboring carbon with a proton on it then right next door all draw the same molecule and then after a draw on these 2 molecules in an identical wh the mall modify them so we can pay attention to the effects of differing spin of neighboring protons "quotation mark tightening for those to be ages and for those to be lines there we go there could be a Tuesday OK so that 2 protons the happy little neighbors I would describe their relationship is this additional remember we talk about this and all that Clerides in the separated by 3 bonds if you walk between 1 or the other and the money going and note that if we were to try to focus on this Proton right here on then we have to wonder whether the proton it's next door it's been up or spin down and so I'm going to a arbitrary aligned these the spins here 1st of all we draw a magnetic field you're in Amman magnet that's this huge magnetic field created by a NMR machines that superconducting electromagnet and now 5 were wondering what the chemical shippers Proton is going to be a whatever that chemical shift is if it was originally the chlorine is going to do shield this Proton and so maybe the original chemical shift might be here but when we take into account that this Proton might have a chemical shift that's going on by the opposing war with the magnetic field is going to lead to 2 possible states is either going to subtract a add to the overall magnetic field and I think I've already Johnny backwards but don't worry about that so in other words I'll have 2 different this this Proton Yemeni circle it so I can be clear which Proton we're looking at this Proton that I circled now will end up with 2 different chemical shifts because it's affected by 1 of the peaks will be higher by a certain amount by certain frequency the other people in the lower by a certain frequency from the original value and we call this difference this this change call that splitting and so you can see how you end up with this double its splitting pattern because there 2 and only 2 possibilities here so again the populations aren't exactly 50 per cent because the animal Armagnac tips this it's like 50 . 0 0 1 per cent in 49 . 9 but you'll never see a difference just by looking at those 2 peaks so that's a classic double splitting pattern and for all intents and purposes the ratios of those 2 pieces one-to-one so that's what causes you to see double its Proton and lost factory and on the relative scale of the Armada distance between those 2 little peaks looks tiny Tom so magnifying here really amplified up the spectrum so a typical range of coupling constants on that and that's the distance in here the distance between these 2 peaks we call that the coupling constant and that coupling constant we use the symbol J to symbolize and that's typically equal to somewhere between 1 in 15 herds and it is independent of the magnetic field that coupling is caused by a proton not by him and Annamari Armagnac machine because it's caused by a proton that coupling that that difference in chemical shifts it's totally invariant an independent of which type of magnet you use so we always characterized this splitting in hurts not in parts per million it's not created by the environment created by neighboring Proton so it's going to seem weird to you that we always list chemical shift in parts per million but we list these coupling distances in Hertz on you simply have to get used to that and I'm not sure when to do so much with with coupling constants in this quarter but that's kind of an advanced concept OK so let's imagine a system that has to neighboring protons I've explained how complex it can be with 1 neighboring Proton on let's talk about a system with 2 neighboring protons and so once again I'm going to start up by drawing my In my animosity that actually here and that's good and redraw this to carbon systems and here's the proton that we're going to 2 to discuss radiologist will draw right there and now I'm going to have to draw 3 different scenarios for use on Monday dropped 3 of the same molecule Over and over and over again there we go and this has neighbors there's going to be neighboring protons not just 1 neighboring Proton but to neighboring protons struggling to squeeze those in here and so here's my other neighboring molecule it's got a neighboring pretend number 1 in neighboring Proton number 2 and over here and my 3rd knowledge of that neighboring Proton number 1 in neighboring Proton number 2 and I'll show you why there's a 4th possibility that we're going to have to consider so once again that's imagined they were in this huge magnetic field created by the Yanomami admit I think physicists use some sort of symbol like being knocked her something for to represents the strength of the magnetic field and I'm not that sophisticated OK so here's our opinions so here's our but the pro-autonomy circle the proton that were looking at 2 were really interested in what's the chemical shift of this is going to be affected by its neighbors and the sticker a look at the possibilities as we look at the various molecules in our collection of zillions of molecules spinning and tumbling around what are those possibilities so 1 possibility is that is that both of these protons on heads have chemical shifts sorcery have suspicions that both line opposite the NMR magnetic field and so the both subtracting in the same way the other possibility is I have a proton it is speeding up and the other Proton been down and so in effect will cancel each other out it's like Proton doesn't even have any neighboring protons because these 2 neighbouring spins can cancel each other out and there's 2 different ways you can end up with that scenario so right below this molecule I'm going to redraw that same situation 2 cotton and it has a neighbor with 2 protons attached there's 2 different ways they had that scenario and were focusing in here on this this Proton that I've circled because I don't want to get all confused and look at the protons that arrows on them and so now when I look at these possibilities there's another way that these 2 protons instead of having the top Proton would spin up maybe the top Proton cadets spin down and then if this neighbouring 1 on the side here has been up that another way that they could cancel out so there's 2 equally probable ways in which the neighboring protons can cancel each other out with their spin With the quantized spins that can only be upper down and then the last possibility Is it both of these protons will have on instead of both protons with spin down there will have a spin conventional adding to the to the magnetic field of the Magna so 3 possibilities and are not equal the middle possibility where the 2 programs cancel each other out is twice as likely as the 2 scenarios on the end so what I'll end up with his 3 peaks in my animosity and those 3 peaks will now look like this so so the circled pink Proton here instead of looking like 1 peak will look like on the destroyer little a little midline here To so I could see what that pink Proton would look like if there was no neighboring Proton so 1 possibility is that these 2 protons or subtracting 1 possibility is that these 2 protons or significantly adding and the middle possibilities that they're canceling each other out and the ratios of those peaks will be 1 2 2 2 1 immediate and do a good job of drawing them where they look like they have the peak area so that a classical triplets and I know it's a triplet because the ratio of peak areas is 1 2 2 2 1 and it's caused by these neighboring protons and we characterize this splitting the the magnitude of the splitting with once again with With this variable J or coupling constant and so if you wanted to measure the coupling constant there the effect of this neighbouring Proton you'd measure either from the outer peak To the beginner peak or from the begin repeated the the four-hour repeat there and again
that's going to be some coupling constant Jade it's measured in hertz OK you can have more neighbors into neighboring protons right to careful hearts of favoring Proton so you can imagine how this complexity can build up very rapidly to take 1 simple signal this 1 pink Proton can be Split into 7 8 peaks no problem but you find lots of spectra were single proton gets Split into into many yes was you on in I'm peering adhered to hacking remember whether I touch it tells you a lot actually just tell you until you want to things if you're coupled to a proton and say so the question is what is tell you so your couples and we're not going to go to this detail you don't need to to worry about using this information J is that the magnitude of J. depends on 2 things appear to protons coupled on the same carbon atoms the coupled to each other you're feeling each other's magnetic field the angle between these 2 2 protons controls Jr so if you're clever you can use J to learn something about the angle between the top to protons if you're on to protons around neighboring carbons in affecting each other's magnetic field it's the torsion angle between those 2 protons like this you get maximum coupling when the 2 protons are empty pair plainer Oracene .period playing you get 0 coupling if the orthogonal a 90 degree torsion angles so taken advanced classes spectroscopy you'll use that coupling constant information to learn about torsion angle and the shape of your molecules and you won't do that in this class to advance the it's so hard just to get a grasp on simple coupling patterns but that you won't be able to well I say that maybe you will ever be on rise you could start taking that stuff into account focus was good and talk about the various common all the arrangements of protons when do you expect when our protons close enough to affect each other so here's argued the 3 coupling scenarios 1 common couplings scenarios 2 protons in the same carbon and these couplings are typically around 15 hurts but as I just told you it depends on the angle between those 2 protons In other words that seem to me that looks like a big coupling it's a coupling where you can see right through those peaks and the animosity factory sometimes the peak the little picture so close you can't even tell that there's 2 peaks there it's hard to tell OK that's 1 coupling scenario where they're close enough to couple the 2nd coupling scenario where the on neighboring carbons we would call that visible coupling enough I count how many bonds between these 2 protons 1 2 3 bonds so that the 3 bond coupling and this varies hugely depending on the torsion angle so 3 to 12 hurts right so in other words that best it's almost as big as a gentle coupling to bond coupling but at worst it's almost 0 so it can be very small and hard to see that couple so I typically would call this a 2 bond coupling original couplings and I wanted to close the 3 bond coupling so if you hear me refer to there's a 3rd type of coupling and it's rare in its small and I don't think I would ask you expect you to know this 1 but but you might see it in some Panama spectra and wonder why is that there so when you have Proton separated not by 3 bonds but by 4 bombs in this arrangement where has the shape of a W sometimes some people call this W. couplings you can sometimes see a small coupling and it's small it's not like 15 her admitted black it's not like 15 hurt it's not like 12 herds it's usually less than 2 so we knew that this is the sort of W shape those 2 protons can couple to each other In 5 bonds knows you don't worry about that and so let me just say that this for bond coupling is rare but you might see it and I don't think I would purposely gave you a spectrum that hedge for bond coupling in and I feel like I might have seen that in some of the lab spectrum but I'm not sure so mainly you just worrying about 2 monetary bond couplings you're going to find a proton NMR this it is this difficult to use spectroscopy at 1st it will take time to acclimate to that OK so we measure coupling constant we we assigned the variable Jay and it's not like you doing the math with that of ICJ value you'll know and talk about a coupling constant and you can have different magnitudes sometimes easier to see 2 peaks sometimes there's the coupling constant is so small it almost looks like 1 B OK so when will you see coupling and when will you not see coupling and rules to remind you of equivalent protons don't displayed each other why and we don't need to go into to the profound nature that the point is equivalent protons don't Split so here is an example of a situation where where magnetically equivalent protons protons had exactly the same chemical shift don't splitting each other so if I look at this molecule these 2 protons or identical as far as the AMA's concerned Bill exist as 1 people and they don't splitting each other you don't see any splitting by those 2 protons even know they're on neighboring province so no splitting here actually that's not the most common case Recinos splitting the most common case Recinos splitting is a methyl group In every case the protons and a methyl group or equivalent so these always show is a 3 h single it whenever you have a methyl group so that 3 Ch and watch this summer nite the letter S there means singly they don't splendor equivalent so in Area C A 3 h single but usually a towering peak in your remark on the 2 I can't think of any case where that's not a methyl group but could design 1 in theory on OK so here's a case but these 2 protons here just 2 protons Iranian deal topic there's no difference between those in a in a proton NMR spectrum they don't Split each other soldiers would write that he these 2 protons don't Split these 2 protons here they don't Split and these 2 protons here or actually this group of protons here they don't splitting each other but what I wanna do is talk about this Proton over here the OH hydrogen bonded protons don't spend all their time attached to 1 hand very well the kind of hydrogen bond this group over here and attached to me and the hydrogen bomb and then attached to me on the time BNR experiment after pulsed with energy that Proton is moving back and forth hydrogen bonding with lots of other stuff in solution before I finally give my energy back and as a result of what you find is that each bonded protons almost never Split their neighbors and I say almost never in no case in this class what I give you a spectrum because would be weird where the OH which is capable of hydrogen bonding but would split the neighboring protons so it is that the NRC section from for we have these 2 appear because they're identical they don't spread each other these would exist is 1 Pecos singly at 4 . 5 parts per million in other words they're not being split by the OH that's because wages will be hydrogen bonding with other of molecules just like itself in solution and this OH over here would exist as 1 peak not Split by this the 2 majors is nearby at 3 . 2 parts per million so you have to look out for for ages attached ahead or Adams because those are the 2 hydrogen yes question could you say that a little louder please the why the Split 0 0 that's only United draw the rest of the molecule the rest the molecule upstairs Janik centers and if the user chemically in equivalent the at depends on what attached here if I if vise I should adhere to bromine and chlorine with amendments which high school so it depends on what else is attached here so maybe like an example of of gentle compound that would have been an example of a general pair protons would split each other is a rain there's a chlorine on the
bottom entity beetle group Equatorial these 2 wages are now not equivalent 1 on the same faces chlorine regions on the same face as the TB group and those 2 now chemically different and they will splitting each other so I didn't draw the rest of this molecule it depends on what's attached case so In again so there was so it's going to keep be talking about this splitting thing yes Saigon I'm so we talked about this issue of to a topic and dies during topic protons and aren't you topic protons are magnetically equivalent the right they give identical chemical shifts by a mark on the Intermarket experiment cannot distinguish between entered topic protons so because these 2 protons are endangered topic on they occur with exactly the same chemical shift and so they don't affect each other and that I'm on not we can't go into the origin of that effect right here with you could move on at the distance but each other it's equivalent protons do not splitting each other they have exactly the same chemical and thank you for asking those questions because everybody is is that even if I'm not ready to go into the details behind that and everybody else wondering the same thing this this tiny little effect that I saved for last great we've covered 90 per cent of a but this tiny little effective splitting is what makes Proton so challenging on and will create most of the work for you in terms of interpretation OK so let's talk about this simple and plus 1 splitting Well we don't you don't need to draw these diagrams with Proton neighbor spin up and proton neighbors pinned down it's far simpler to analyze splitting patterns just by using an empirical rule called the end plus 1 splitting were so it not of this the rule is very simple assess any equivalent neighboring protons give n plus 1 peaks so in an equivalent living so here's an example where I'm drawing the 3 carbon system and I'm not drawing with the neighboring With the the neighboring groups are what simply doing isn't simply telling you that there are no protons here no protons here no protons here no protons there In this situation where there are no neighboring protons 2 bonds 3 bountiful for bonds away this would appear as a single as a single so the number of neighbors here it's just right number of neighbors a 2 3 or 4 bombs away here 0 so according to the end plus 1 rule 0 plus 1 batch appears at a single peak a single so sketched out out 0 neighbors and plus 1 it appears 1 p and we call it a single but notes let's take a look at an alternative scenario where there's a single neighboring protons and who cares what the other groups are chlorine bromine maybe it's part of a double bond carbon atoms I'm not going to draw anything any of the other neighbouring Adams we don't care about those I'm simply telling you that in this scenario and there's 1 neighboring protons that's either to 3 or 4 bonds away like this and so then plus 1 will says 1 plus 1 and plus 1 if there's any neighbors 1 neighbor then I had a see disappear this Proton appeared as a Dublin 2 peaks and I didn't do a good job because it would you know the area would be half of each peak but they would add up to as much areas 1 told peak so but I wish I draw on those that shorter and of course we would call this a Dublin that's the sort of nomenclature here so now we're going to take this story of this approach we're looking at this Proton here announced that 2 neighboring protons that either to 2 bonds away 3 bonds away and so now with those of people with those 2 neighboring proton beam plus 1 rule says 2 plus 1 that appears at Tripoli and I don't need to draw any fancy diagrams I just need to look at how count of the neighbors and say Triplett and remember the peak ratios they told you for a tripling its 1 2 2 2 1 In filing draw that that Peak area ratio correctly that I'm not drawing a correct Triplett and you could go on inventing scenarios Reid's 3 neighbors that etc. OK so that you don't need to them plus 1 predicts whether you'll get a single double it or but more importantly the peak areas are predicted by it's something called Pascal's triangle which I think gets from some sort of binomial expansion mathematics on Pascal's triangle you could re-create that simply by adding 1 plus 1 equals no 1 plus 1 equals 2 1 1 plus 2 equals 3 calls for that another some simple addition you can do between each neighbouring pair of numbers that gives you the next row of numbers so what this does what Pascal's triangle does is it predicts for you the peak intensities for all the common splitting patents and yes Saigon for this scenario yeah I didn't draw also let me just invent scenario where it has nothing else there so that you're not so it seems weird that I didn't take the time to draw anything here I was just didn't want to here's what I didn't want to be I draw extra stuff you become so complex by year's Dukla ranges of bromine here's another cut right and I just didn't want to look too busy so the intent was that there weren't any other protons there and I was afraid to draw extra Adams because I thought it would look too complex and so you have to imagine a scenario where there were no extra protons as neighbors OK so OK so good talk about these peak hour area intensities for a single at you don't need to worry about whether it's 1 2 2 1 ratio Singh went on exists as a single peak and all I'm not going to write the words singling anywhere on any spectrum I'm simply going to write S it that's meant to understand that that that the peak singly and not to peaks that are close to each other when you see 2 peaks with a tiny peaks in 101 ratio that could be a Dublin and all symbolized that with the letter D and the 2 peaks will of course be nowhere close to a one-to-one ratio and if you see 3 peaks if it really is a triple-A we would symbolize that with the letter T and those peaks for the statistical reasons I showed you should appear in a 1 2 2 1 ratio and finally if Wal-Mart finally a quartet to see how the language works which symbolize with the letter Q those'll exist the peaks will appear in a 1 2 3 2 3 2 1 ratio if they're not approximately 1 2 3 2 3 2 1 then I would worry that maybe that's not a regular and you can keep going all the way down to a post-Sept actor with 7 peak or or more so finely you'll get to some scenarios where there's so much splitting in so much coupling going on that you simply can't interpret and it's very common and quite often we simply just throw up our hands and say that's a multiple at nite I don't know how many pizza in there I can't even see between the peaks there's there so crowded and we symbolize that within them and that means I've given up trying to assign how many pizza actually in that that little forest of peaks that yes on this because in this scenario this is all due to a single proton the area under here has to equal the signals given off by a single protons and so here this is given off by single proton so in other words a single it might have an intensity looks like this on but a quartet even the area adds up to the same end will look smaller but if you had a period would be exactly identical because it would arise from a single protons in the spectrum because this could take a look at a real spectrum that is splitting mentioned this came right out of the the Gaussian ski Smith textbook its stake pain and this is quite common so if I look at the spectrum in the blue background here at this
peak that's located around 5 . 9 parts per million of it's kind of hard to tell what's going on there the pizza so scrunched together so quite often if somebody doesn't tell you how many pizza there they might give you an expansion so see how they've expanded here so you can now see I see 4 peaks and look how satisfying that is the president in a 1 2 3 2 3 2 1 ratio as a quartet that's not just for peaks that happen to be close together I bet money that that's a court tho I know it's a quartet you and uses of the and then there's this other peak where you can't quite tell by looking at the Blue tiny spectrum is that 1 Pekar 2 peaks close together but when they give me the expansion you can see daylight between those 2 peaks it's definitely on to peaks not 1 peaks of 2 peaks in close together and those 2 big servers a Dublin pretty clearly that you know the peaks at exactly the same height on but it's pretty close to 1 2 1 2 speech peak ratios for quartet 1 2 3 2 3 2 1 on hand for a double one-to-one ratio ratios so what's going on here so the proton disappearing farthest downfield at 5 . 9 parts per million is at the Red protons or is it the green protons the appearing here at 5 . 9 it's the green Proton that's closest to the elect these will these selected made chlorine atoms a D shielding that Proton sort of sucking electron density from around it so that's the proton here that's that's appearing at 5 . 9 parts per million and so why is it appearing in the Quartet the reason that appearing in the Quartet is because come on this is because red protons or splitting that and there's 3 of these red protons and according to the end plus 1 rule so let's look at the endless 1 Wallstreet plus 1 equals quartet we could have predicted that this green Proton is the farthest downfield and it's being put into a quartet and you could have predicted with the spectrum would look like ahead of time OK let's come over and look at the CH 3 groups if I look at the integration in this this lame integration line here if I took out a ruler and measures on that would correspond to some sort of area under the integration mine whatever however for up I go with my integration mind it's is 3 times higher then I went out with this first one that corresponds to the fact that the area under these 2 peaks is 3 times bigger than the area under these 4 peaks and that that methyl group is not shifted is far downfield this carbon is now 1 carbon further away from those 2 chlorine atoms muscles protons on D shielding anywhere near as much and why is it splits into 2 pieces a double at its splitting into 2 peaks a doublet because this little Proton over here that's 1 proton and plus 1 1 plus 1 equals 2 Dublin so again the end plus 1 will predicts for you this sort of splitting patents singly doublet triplet when you look at an enema spectrum it would take a look at another example it is splitting and again this is I think this is a figure that came out of the book I can't remember where I got this OK so now and we have a compound it's highly symmetrical and the reason I'm showing you this is I wanted to point out but that the protons that heard that the protons are displaying don't have to be attached to the same carbon so that these 2 protons that annexed to the on carbon next bromine there's 4 of them and they're indistinguishable in identical the protons on both the left hand side of the molecule the attached bromine are indistinguishable from the carbons on the right-hand side of the molecule that are attached to bromine so all 4 of these protons I expect to appear as a single signal we now want peak but they all have the same intrinsic chemical shift before you Split them and so on since those are closer to bromine the the protons in the middle of the molecule I expect these 4 protons to be shifted this downfield and hear the odd about 3 and a half parts per million and very nicely there's an insect for you that allows you to see from those for protons so here's my signal it's for age it's 0 for each signal is for protons in their user protons B and they're being affected by their neighbors this siege to group there's 2 protons there the end plus 1 will tells us that these will will split these protons here will splits this for each signal into 2 plus 1 equals Triplett it's amazing even the least these 4 protons aren't all attached to the same carbon they still are affected by this neighbor in the same way following the end plus 1 so that I would call that a for each triplet that's the way you would abbreviate that in an hour spectrum for age ,comma I italics to reside italics for singling doubling tripling so now it's walk over here this week To the CH 2 group in the middle of the molecule and think about that in the end you can see that signal down here 2 . 3 parts per million so we think about what kind of splitting pattern we expect to see if we look over here there's a set of peaks that the expansion 1 2 3 4 5 5 peaks Pentagon and so the what's happening here is that these 4 neighboring protons books maybe I should use the the black can hear these 4 neighboring protons Split this into 4 plus 1 equals 10 10 and if I think about the integration there it should be but to wage ,comma center that's very unusual actually to see Appendix I. but it would be italics P so oftentimes people won't I won't show you the instead of simply write to age ,comma paid to age means you don't have to look at integration my nominee protons are there and I italics P means you don't have to count up the peaks on To know that that's an actual Penta populist wouldn't talk about the sombrero I that looks like I was ready to talk about some variations in In the magnitude of coupling and splitting it OK so the coupling but that as I already mentioned that the coupling constant it depends on angles so the actual angle here between 2 general protons will cause the coupling constant not to be 15 herds that's kind of an average number put to vary between 12 and 18 hurts I'm still 18 Hertz is a pretty big coupling but there is an exception to that well maybe not an exception but if you really stretch this angle out to 120 degrees so that's what you'd that's the angles that you have 1st substituent honestly to Avoriaz carbon 120 degrees at 109 for S P 3 hybrids carbon knowing you will expand that angle out the coupling starts to get very small she can see here for the 2 wages at the end of the CC double bond sometimes is very hard to see the coupling at all so the angle matters a lot so be careful before used to say that hour before you claim that there is no coupling there because it might simply be a siege to it that at the end of a seedy double bond on so visceral protons the maximum coupling Levasy is when to proton Tahiti period cleaner to each other and that can be up to 18 herds in value when the 2 protons or soon will be a little bit smaller a very typical coupling constant like the ones you saw in the last spectrum that that the sort of distance between peaks on has to do with rotate all bonds so most typical range for coupling constants that you would see when you see splitting patterns between those tiny tiny splitting patterns between peaks is about 5 to 7 heard 7 Hertz is probably the most common average coupling constant you'll ever see rotational bonds like that I don't believe I'm going to show you any spectra that involved on that involve you analyzing those different coupling patents on so don't worry about that but it
sounds like everybody's picking up to go that means we haven't finished the proton and amount trying to finish up the last bit on Wednesday found that try to do is you should be able do almost all the problems in the sapling work based on the stuff that you've got right now
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Metadaten

Formale Metadaten

Titel Lecture 19. NMR Spectroscopy, Part 3.
Serientitel Chemistry 51B: Organic Chemistry
Teil 19
Anzahl der Teile 26
Autor Vranken, David Van
Lizenz CC-Namensnennung 3.0 Unported:
Sie dürfen das Werk bzw. den Inhalt zu jedem legalen Zweck nutzen, verändern und in unveränderter oder veränderter Form vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen.
DOI 10.5446/19488
Herausgeber University of California Irvine (UCI)
Erscheinungsjahr 2013
Sprache Englisch

Inhaltliche Metadaten

Fachgebiet Chemie
Abstract UCI Chem 51B Organic Chemistry (Winter 2013) Lec 19. Organic Chemistry -- NMR Spectroscopy -- Part 3 Instructor: David Van Vranken, Ph.D. Description: This is the second quarter of the organic chemistry series. Topics covered include: Fundamental concepts relating to carbon compounds with emphasis on structural theory and the nature of chemical bonding, stereochemistry, reaction mechanisms, and spectroscopic, physical, and chemical properties of the principal classes of carbon compounds. This video is part of a 26-lecture undergraduate-level course titled "Organic Chemistry" taught at UC Irvine by Professor David Van Vranken. Index of Topics: 00:38- The possibilities of 3D printing 01:02- 3D home printer 02:23- Meltable Polymers for Low-Cost 3D Printing 04:57- 14.6: Coupling between nuclei leads to splitting of peaks 11:28- 14.6A,B: Analysis of Doublet and Triplet Splitting Patterns 23:00- 14.6C: Splitting Rules 32:02- 14.6C: The n+1 Splitting Rule 39:35- Splitting Example #1 43:25- 14.7: Example-Two types of Protons 46:59- 14.8: Variations in the Magnitude of Splitting

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