Lecture 10. 13C NMR Chemical Shifts

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Lecture 10. 13C NMR Chemical Shifts
Chemical Equivalence and Spin-Spin Coupling
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Lecture 10. 13C NMR Chemical Shifts
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This video is part of a 28-lecture graduate-level course titled "Organic Spectroscopy" taught at UC Irvine by Professor James S. Nowick. The course covers infrared (IR) spectroscopy, mass spectrometry, and nuclear magnetic resonance (NMR) spectroscopy, the latter of which is the main focus. Topics covered in the NMR spectroscopy part of the course include chemical shifts, spin-spin coupling, dynamic effects in NMR spectroscopy, and 2D NMR spectroscopy (COSY, HMQC, HMBC, TOCSY, NOESY, ROESY).
Sense District Kohlenstoff-14 Spectrometer Chemische Verschiebung Intergranular corrosion Methylgruppe Chemistry Kupplungsreaktion Alpha particle Ethanol Molecule Beta sheet Hydrophobic effect Process (computing) Conformational isomerism Vimentin Carbon (fiber) Chemist Protonation Chemistry Kupplungsreaktion Wine tasting descriptors Emission spectrum Hydrogen Nuclear magnetic resonance Magnetism Azo coupling Methylphenidate Nucleolus Gene duplication
Sense District Thermalquelle Ester Resonance (chemistry) Memory-Effekt Aromaticity Organ donation Silicon carbide Alpha particle Nuclear magnetic resonance Sample (material) Deterrence (legal) Alkalinity Electron Phenol Beta sheet Flux (metallurgy) Halogen Hydrophobic effect Setzen <Verfahrenstechnik> Coiled coil Stickstoffatom Octane rating Carbon (fiber) Protonation Spawn (biology) Elephantiasis Kupplungsreaktion Electronic cigarette Wine tasting descriptors Emission spectrum Kalisalze Functional group Ems (river) Nuclear Overhauser effect Cobaltoxide Carboxylierung Modul <Membranverfahren>
Ionenbindung Chlorofluorocarbon Ester Sunscreen Set (abstract data type) Wursthülle Aromaticity Chemistry Nuclear magnetic resonance Molecule Lactitol Cycloheptatrien Gap junction U.S. Securities and Exchange Commission Setzen <Verfahrenstechnik> Agar Carbon (fiber) Topicity Carbonylverbindungen Protonation Adenosine Kupplungsreaktion Electronic cigarette Emission spectrum Hydrogen Magnetism Functional group Azo coupling Acepromazine Chemical compound Zunderbeständigkeit Carboxylierung Base (chemistry) Medical history Distillation Gene duplication
Chemische Verschiebung Aluminium Hydrochloric acid Chloride Operon Memory-Effekt Optische Aktivität Molecule Dreifachbindung Lake Rapid U.S. Securities and Exchange Commission Doppelbindung Octane rating Concentrate PEEK Chemist Katalase Multiprotein complex Alcohol Biphenyl Wine tasting descriptors Electronic cigarette Paste (rheology) Acid Azo coupling Thermoforming Chewing gum Stuffing Ionenbindung Reaction mechanism Sunscreen Economic sector Wursthülle Methylgruppe Reflexionsspektrum Sample (material) Inflammation Lactitol Stream bed Sea level S-Adenosyl methionine Pain Body weight Oxide Process (computing) Cell cycle Flame University of Porto Semiotics Stickstoffatom Chloroform Carbon (fiber) Protonation Chemistry Kupplungsreaktion Water Hydrogen Ice Functional group Carboxylierung Deuterium Distillation National Rifle Association
Homocysteine Lactose Chemische Verschiebung Chemical plant Angular mil Ethylbenzol Wursthülle Reflexionsspektrum Alpha particle Klinisches Experiment Molecule Fire Ageing Methanisierung Altbier Phenylalanine International Nonproprietary Name Zinc S-Adenosyl methionine Setzen <Verfahrenstechnik> Nitrogen fixation Topicity Carbon (fiber) Protonation Biphenyl Emission spectrum Hydrogen Functional group Chemical structure Gemstone Ganglagerstätte Deuterium
Metal Ionenbindung Diamantähnlicher Kohlenstoff Elektrolytische Dissoziation Biofouling Protonation River source Essigsäureethylester Molecular beam Kupplungsreaktion Alcohol Methylgruppe Alpha particle Molecule Island Acid Functional group Azo coupling Tablet (pharmacy)
Metal Setzen <Verfahrenstechnik> Ionenbindung Blood vessel Operon Chemist Carbon (fiber) Topicity Protonation River source Kupplungsreaktion Methylgruppe Nuclear magnetic resonance Molecule Emission spectrum Hydrogen Functional group Azo coupling Explosion Cobaltoxide Separator (milk) Deuterium Methanol
Our today we're going to talk about 2 different things we talked about proton chemical shifts and today I want to talk briefly about C 13 on a martyr shifts will talk more about them later on but then were going to start and we're going to spend a reasonable amount of time talking about spin spin coupling and in order to understand this we really have to to understand the concept of a chemical equivalents which ties into concepts of symmetry and stereo chemistry and conformational analysis since really beautiful chemical equivalents and so will be talking about chemical equivalents in spin spin coupling were actually going to be spending a good deal of time because there's a lot to understand it gained as you can already see from the problems people were saying Hey what's going on here and these problems these very simple molecules have all sorts of cool issues of spin spin coupling and all sorts of cool issues of very chemistry wrenching as spend number of lectures on them next time we're going to develop a concept called magnetic equivalents which is different which is of an amplification chemical equivalents but it's too much to take in 1 and then we're going to spend a couple of times talking about details of spinster couple part while I want to say about carbon atom spectroscopy 1st art if prone to earn in was difficult because you have a very small population between your alpha and beta states carbon in Amara is even worse in 1st you know that carbon 12 doesn't have an NMR spectrum it's not actively doesn't have a magnetic dipole and we only have 1 per cent or more specifically 1 . 1 per cent see 38 so most of your molecules for small molecules don't contain any seat for small-molecule some of them contained 1 sees that the now things get worse the Magneto gyrate 13 is only a quarter of that all of the many Riccio for Proton and now remember what the implications are a fact that means that you get roughly a quarter from use children to save approximately a quarter of the Boltzmann differences send difference in Boltzmann main distribution in alpha and beta states 4 so already we've got fewer nuclei that can work but to put it another way of 500 megahertz spectrometer gives you a carbon spectrum at 127 . 5 megahertz here over a quarter because he is a hero of for court things did get worse than that you .period hold is only a quarter as strong yes What if you want generates an electric current like a generator you want a big honking magnetosphere Proton is a little magnetic but carbon is a tiny magnets because it's about a quarter of the magnetic dipole so you're damned began and then you further get failed because the procession ready it is also a quarter of seats for Proton at that same 117 thousand 500 doused magnate your possessing at 500 times per 2nd for carbon your only possessing at 125 that million times there's a thousand billion times per 2nd so that also gives you a quarter as much electricity in the corner so you got 1 . 1 per cent at a quarter of a quarter of a quarter which means you're only 1 500 won the 5 thousand 800 and sense of question the Villamor frequency so if you want if you take a magnet just spend it if you spend it faster you get more voltage you get if you spend twice as fast you get twice as much which if you take a magnet that's twice as big you get twice as much for too and so for all of these reasons and you've got In addition to a smaller magnet you've got fewer than because you've got even if you give a 90 degree pulse you get only a quarter of the magnetic dipole from having only a quarter as many nuclei going down into the export work all it is it's it's a core of compared to Proton is so common is a much less work of much less sensitive technique than Proton and lost us now there were few redeeming features so 1 thing that's redeeming is weak typically do Proton decathlon 4 so normally of Harbin would be selected by all of the protons so for example the carbon in ethanol would be slipped into a quartet in the carbon in the methyl group of ethanol would the splits into work or attacked by the 3 hydrogen instead are attached to it and then it would be further supplied by the hydrogen is overrun the muffling Kaka but what we do is we radiate the proton so all the common you're going to see virtually all is called Dundee coupled card that flips the spins of the protons rapidly which means the carbon doesn't see them as being upper spin down sir cobbled carbons appear as a single well that's good because that means
all your common single signal is gathered 1 peaks so that gives you more than the other thing is when you do that's actually use single Let's which is delighted shopper the euro and the other thing it leads to is what's called the nuclear over houses it will talk more about this is a technique but the basic principle of the nuclear over Hauser affected by perturbing the alpha and beta states of the core of the protons you end up enhancing the difference in Boltzmann population between elephant beta state of departments of actually gives you a big fish so all of this leads to a better signal then you would otherwise get in a hotel and on the couples are anyway suffice it to say nowadays it's easier to collect the carbon in Amara spectrum it typically will take more sample so you can collect a proton and a sample 1 strict knowing and use a milligram of material or even intensive milligrams for carbon you might want .period 30 megs Indiana module before you have a chance Clinton would attend you could do it at a milligram but it takes a lot more more time I remember if you have 1 mg verses at 10 mg it's going to take a hundred times as long to collect the state saying signal-to-noise ratio which means if you're new research labs and you have some sample it actually makes sense if you're trying to collect the carbon spectrum to weigh your sample released the cognizant of how much you put neuron too because you want to get spectrum quickly and you want to get the signal-to-noise ratio it also makes sense when you're filling your animal are 2 to only fill it with the appropriate amount of work on the coil brokers is 3 and a half centimeters a requires a 3 and a half centimeter high sample at half a so if you dissolve your sample don't dissolve it and no 1 here don't try to be clever and dissolving . 3 males because then you mess up positions on the spectrum because you flux lines at the end of this year saying that that's the way to get that far I want to talk about where the peak show up so Colorado Morris spectrum the carbon in more spectrum has a big ratings typically from about 0 to about 200 200 part of 20 to 40 aliphatic show up at about 10 to 40 someone big ratings of 2 hundreds Urso ppm that's in the outfield region "quotation mark carbons next to an electron withdrawing Adam show downfield but it's not quite as pronounced so ,comma next halogen you might even sort of seated in this range carbon extra nitrogen is going be sort of at the end of the day but by the time you next to an oxygen is an electron withdrawing rebuked I'd say 50 to 70 carbon next to 1 of oxygen so that sort of stands out Alpine sorry that comment by memory centers about 2 and a half parts per million 2 . 2 parts per million maybe for a typical alkaline C for an alkaline carbon it's about 70 to 80 ppm so that kind of stands out alright Elkins and aromatics where is in proton NMR the Elkin shop little more upfield 5 to 6 and aromatics a little more downfield O'Kane said aromatics are also the 1 about 110 Beyond about added costs typical values if you put on oxygen on an aromatic like but at a solar phenol where you could not oxygen directly on a carbon that carbon might be 160 parts per million if you had a very electron double talk more about specifics ship but you could easily have if you have high electron donations in author carbon you could easily be a well below 100 alright ,comma meals esters and carboxyl since you get a little bit of a resonance effects that they show up a little bit less for some of the others let's say about 170 to 180 parts per million out of hide show up a little further down the field let's say about 190 to 200 ppm and she intones I'll say or a CEO are primed for a key towns let's say about 205 to about 220 lastly I just wanted to give you 1 will hang in there by the way if you ever miss your hand out certain misplaced them I put them up on the Web with the video part of the course so you can always go ahead and download downloading 2 Our it's just as I had my say when Elsie was just as I had my goal pigeon drawings of might take a moment to look at in mediating a proton NMR spectrum I have my little pigeon drawing of what to take we you want to look at when Eugene C. 13 Morris not words this type of region is aliphatic exterior apartment next significantly
withdrawing group like an and out of an oxygen here's your Alpena
aromatics here's your esters and endured al-Tuffah the heightens in Quito loans so to a large extent it's sort of like H 1 in tomorrow but when it may be a factor of 20 on this scale in other words most of what you're going to see in a proton tomorrow is from 0 to 10 most of what you're going to see the carbon and mother is from 0 to 200 carboxyl tacitly further out the tones of the further after that kind of kind of gives you my read things are there should be a you the basics To start to use carbon in Amara in helping to analyze some of the homework
sets that we're going to get so 1 thing that you can get is a reading of things like carbonyl groups and they are another thing you'll be able to do is to count out and see how many different types of that because where In proton you may have overlapping resonances most often because the carbon spectrum is more dispersed and peaks typically show up saying Let's most often you will see be able to see 1 key for each type of art I wanna talk now about spin spin couples was ends if I had to give you a very very general way of thinking about it the way our described and we're going to see amplify on this in today's fall off the way that I would describe it is that protons that keeps splintered by adjacent protons that are different move later on amplifier the concept of adjacent talking about to bond coupling 3 bond coupling and warm tougher line but today what I like to amplify on it is the concept on the same and specifically if so let's start with an example that very very very into it very Vernon freshman some more the chemistry let's take the H 1 and more spectrum of coral and so my little pigeons statue of the spectrum Coro FAA would look something like this we have a 1 2 3 2 3 2 1 trip led somewhere down field of 380 ppm were just a hair downfield 3 ppm and then we have a one-sided 1 2 3 2 3 1 4 10 and then somewhere just a hair down field of we have a 1 did you 2 1 trip the Triple-A comes of course from the CH 3 and I can say that in this particular example CH 3 losers led by the adjacent ch tourists and I can say because the 3 hydrogen ends of 12 let's talk about the CH to the ch to are selected bye the CH 3 the 3 protons all the CH 3 girls are this was saying that the CH 3 there is not when each other I'll say the CH 3 protons did not say when teachers and then I'll say in this particular case this is do not display it each other In other words in this particular case the 2 hydrogen use of methylene group of artists saying so they don't splitting each other but more in general on give this as an exception so if you're compound has a Carroll center and the war the protons or otherwise history a topic then they most likely to and so this success is something that we're going to be playing with in today's lecture the right before we come to this very an important concept of dire stereotype let's tackle this basic notion of the 1 2 2 2 1 would and the 1 2 3 2 3 2 1 quartet so we have a transplant In this wanted to Tudor it comes from the Ch 3 and it the CHT In the 2 protons act as will magnets each molecule and those little magnets can be stand up 1 can be spent up and 1 can be stand down or they both can be spend at sea get everyone there is 1 way for them both to be stand up there are 2 ways for them to the 1 they up in 1 state on their own and there is 1 way for them to be spent out and so that gives rise to are 1 2 2 2 1 triple for a quartet we have a 1 2 3 2 3 2 1 ratio the quartet of course comes from the CH 2 the CH to seize the CH 3 and all of the protons can be seen on some of the molecule say saying there are or to get me stand up and 1 can be staying down there are 3 different ways that that can occur lot 2 can be stated only 1 convinced about and again the
3 ways that can occur were they all can be suspended we can generalize this idea to say if there were any the wall and I'm going to underline equal couplings we need to In plus 1 lines so there for equal couplings you get 5 lines those 5 lines of follows Pascal's triangle you can work out the statistics yourself or you can say that those those fine wines and of being in a 1 2 4 2 6 2 form 2 1 ratio and so forth you basically at the ones above or you work out workout the statistics so for example if we go show I said pro-coal chloride now the CH here it's equally by 3 methyl groups so the CH appears as a a TAT and the ratio of the lines are 1 2 6 to test 15 to 20 to 15 6 2 1 and because the quartet because the sector is going to be very small compared to triple its import cats molecule unless you look hard you might not see these lines on the outside and backed by the time you get up debris big multiplex like Sept texts and so forth text often people will just reported them as a multiplex in reporting losses I let's take case a look at a case of what I mean by couplings that may or may not because the so I mentioned the Masire Group in like specifically investment from angry so this find group is working by 2 methyl groups it's also displayed by this the Smithsonian and so depending on whether the couplings are equal that is whether the coupling constant certainly while it may be enough tapped the more it may be more complicated and I can tell you from experience in this case it would be more complicated than it would be in this case the government of Sept texts which would probably report was involved the OH of alcohols and I know this is already come up on the homework no weights of the alcohol Mayer may not couples so the hydrogen device a proper No Limit line of ice appropriate all my appearances said the more work it might be more complicated In order to couple this hydrogen the stick around in 1 place has to stay attached to that Proton for a time that's roughly 1 over the coupling constant another words it has to stay attached since coupling constants of typically on the order of or about 7 hurt it has the state tax for hundreds of milliseconds or a longer effect hydrogen exchanges on the order of tens of milliseconds this month is not going to see it as either spin-off were spinning down it will see an average annual gain couple if this hydrogen doesn't exchange then will be in a situation here and it will see it either as spin-off worries stand down and you will have splitting either as an architect or a doubling of set text sector of upwards depending on the road Jason will get into the lake to collate primary alcohols often exchange rapidly so when alkaline like alcohol at the end of CH to change like you may have in the homework problems usually will exchange rate secondary alcohols sometimes do sometimes don't more steered strictly clear the exchange is going to rate of exchange is going to depend on a number of factors including the concentration of the sample because the molecules can exchange by colliding it will depend on the amount of water in the sample there's invariably advantageous watering your during to bed about 20 mobile or concentration 10 20 30 or concentration and chloroform undergoes photo oxidation to give hydrochloric acid DC In the case of the CDC off and that will rapidly promote exchange so if I want to minimize exchange rate typically will pass chloroform through aluminum fell by simple but McCaw formed through me that I'd ride over a flame that will take out the acid to minimize the water OK so alcohol is attainable wild card online to a couple of hours up do you still see the proton In general if maritime is exchanging with other molecules you will see it and it will be there if the Proton is exchanging with water and you have a little bit of water said all you will see in the air and the water peek at the weighted average of the 2 if it is exchanging Our with Water and there's a lot of water then it will become part of the water also there 2 different timescales What is the timescale for couple the other is the timescale for being able to see if you remember I talked about the uncertainty principle before so in order to see coupling your mind with past beat euro exchange rate has to be you have to to be able to make the observation such that you lined with his own
order of better than 7 in order to not have swapping with water which is very for waste is typically 1 . 6 parts per million or former members and alcohol can be 1 of the 5 parts per million let's take 4 ppm those are hundreds or even thousands of birds away right of 4 ppm difference is 2 thousand hertz so in order to not have exchange with water where you can see the alcohol he it has to stay attached for tens of milliseconds rather than hundreds of or carboxyl against it's a real bad boys in this regard because they do which change rapidly which is 1 of the reasons he typically broadens out for form alcohols often will stay attached secondary means are big pain in the secondary means are almost impossible to see you have base-catalyzed exchange mechanism primary means tend to be a little bit better behaved aromatic comedians are well-behaved some talking aliphatic innings but if you're working on alkaloid project or some other projects knew secondary and you really are in trouble at all the fact is that all the authors of the book I have with it is a unique yes if you want to call it absolutely coupling is mutual now you could envision a circumstance where you had J. coupling but quadruple broke so you could have a hydrogen on and nitrogen that could be broadened to a point where it was abroad Singh but the hydrogen on the carbon could be split by and there the broadening would be quadrupled but guests typically so again let's talk and rules rather than exceptions no technically it's going to be seem both ways sometimes what happens is you may for example if you have a very complex coupling pattern if you do well coupling you may just see this guy as a complex multiplex and then see this guy's a double white because this guy is splitting this guy but it's such a complex splitting that you can't actually discern what the persuading pattern is on the other hand it's the same coupling constant but you only have 1 coupling with them other questions these are really important is it really understanding the real stuff you're going to see them the methyl groups coupled to there's not lot because it's far away in general coupling is going to be 3 2 worth rebalance although fine the case of double bonds and triple bonds you can get couplings there's a very good appendix in the back of your book I forget whether it's Appendix A. Appendix at the back of Silverstein what was the appendix of looked it up in a way that is a very good place to start but in general unless you have a long-range coupling will get to that in a lecture to his that unless you have long-range coupling gentle coupling is going to be be 3 to 4 let tackle the concept of chemical equivalents chemical equivalents is the 1st level of sameness that I was talking about memory said that protons only coupled to other protons if they are different 2 protons are the same are chemically equivalent if they exchanged by a cemetery operator can be exchanged by cemetery operations were rapid process for example rapid rotation about hour are the all caveat this ties into something I I said last time virtually all you can say all rotation about S sp 3 sp 3 carbon bonds are rated at room temperature I'll say virtually always grafted there room temperature that said he see 2 hydrogen splitting each other in the bullfight sp three-province attached to each other chances are you need to think deeper and it's not know there's some slow process are 1 cholera to this is chemically equivalent protons have the same chemical shift so this thing here is kind of like the golden rule of splitting in the basic do unto others as you want others to do once you if you can do this in mind you're going to be very very well set on all of the detail all right let's talk about specific way of thinking about what's the same and once there for 1 way that I like to do what you can do it by a couple of days if you're going to cemetery you can't just go ahead and say or do we have a cemetery operation that interchanges these 2 hydrogen saying diphenyl nothing you can say interchange by reflections and therefore their chemically equivalent what we're going to get into some cases that at least the 1st time you see there are tricky and another way to do it is just to perform a little thought experiments and say are right was the topological relationship to each other and the way you do this thought experiment is you replace 1 proton by deuterium In the
other protons by deuterium and then you ask yourself what is the to relate to the relationship between these 2 molecules and in the case of this particular thought experiment these 2 are the same and since they're the same topologically recall those 2 protons home topic and homotopic protons are technically at war let's try another molecule obviously obviously obviously means a trivia so let's take instead of diphenyl methane saying let's take ethyl benzene and again will consider worse considered the methylene group that fuel hydrogen groups of the methylene broke still exchange fire reflections so if they meet the criteria there there was "quotation mark yeah you can't tell them apart so they have the same chemical shift and 2 protons that are chemically equivalent all are the same and don't square chemically equivalent protons through with each other then later on we're going to talk about a concept called magnetic "quotation mark it's in what you'll see is that although chemically equivalent protons was actually I'm going to I'm going to hold off on this the right now I'm just going to leave it as there are 2 types of sameness and chemically equivalent protons don't each other or if there also magnetically equivalent what we're going to get to that later for now this simple rule is chemically equivalent protons are the same ministers are less trial did not experiment here we replace 1 by deuterium when we replace the other bye deuterium and now these 2 molecules are they the same know where they and an energy and so now they are in Nanty emerged which means topologically the protons are Nadia topic and in nearly 2 years topic protons are also chemically equivalent I said Now let's come to molecules wary have Apparel Center and molecules and since we've been building on this idea of fennel groups and going to give us the molecule phenylalanine it doesn't matter whether I 1 Rossini which we have to to have have whether at 1 molecule OK these 2 protons are now no longer exchangeable by reflection and no matter how rapidly you rotate they still are not the same so these 2 protons now the methylene protons are not chemical plant and let's try a thought experiment here again we can sometimes things can get more complicated than you might anticipate and so it will take 1 replace it with the deuterium and will take the other and replace it by deuterium and will ask yourself what the relationship of those 2 structures is to each other what are they the Dallas-area murders so we say that the 2 hydrogen is of the methylene groups are dire serious topic can therefore they are not chemical "quotation mark the Our said here's a spectrum of phenylalanine so we can see what's what's going on this is a suspected
taking indeed 2 0 with DEC helped the dissolve euro ACL himself so all of the all ages and ages have exchange with deuterium and changing rapidly and for all intents and purposes don't so we see a peak for our HO data and then we see the rest of it or carbons attached to hydrogen we see Arafat over over here and the 7 to 8 range we see our Proton connected to the Alpha carbon Over here just a pared-down fielded about of for about 4 . 3 parts per million and then we see our Bader
protons the ones that are next to the fennel and we see them as 2 pizza he took the bait protons appears at Anthony's or expansions here each of the beta protons appears at this stage positions they're not the same they're not chemically equivalent they could be coincidence meaning appearing the same position but they are not and so they appear at different positions and what's more each of them is a double-edged of doublets where did wife because each of the protons splits the other 1 and displayed by the offer so we have both a J 2 HA expects to bond coupling since you go 1 to bond to get from the stupid protons to each other and we have a 3 bond coupling between the alpha proton beams to the In the alpha proton is also a doubt whether outlets each proton is a doubling of lets the
alpha proton is a double that of tablets because it splits by the 2 beta approach to islands and its played with different coupling constants the beta protons are coupling to the outlook of proton probably with about 6 and 8 hurts coupling constants will be talking more about use in the moment of the future lecture and the date protons her coupling to each other with about a 13 or 14 hurts coupling counts let's talk about why we have to keep our heads attached to us some going to give us another example the example of give us is a molecule called acid foul as a is acid alcohol IT Chi ethyl acetate so what we have here we had a couple of methyl groups and we have a metal Associates the reason of the FL Group the pier here as a Triplette said this is 0 Ch 2 C H 3 that looks pretty
reasonable we have another Mathilde group it appears as a double-edged that's our Ch ch the parade that looks pretty reasonable we have are Miscellaneous it's the 1 that's attached to 2 oxygen so so it's shifted downfield it's at 4 . 6 parts per million it's a quartet because it's slipped by the methyl group and finally we come To the CH In the CH chose show what this stupid it takes a moment to wrap your head around this interact your head around this when you have to realize is that these 2 protons are not chemically as well you can think of this a couple of ways they don't exchange by cemetery operation if you reflect through the plane you don't get the same as another way to think about it I think the easiest way to keep your head on straight is to think about it rigorously you
imagine replacing 1 of them with the deuterium replacing the other half of them with deuterium and the molecules that you get our very murders In other words the 2 protons are diverse the higher helped him into on the side of the state and the best of the season there are absolutely great question just because 2 protons are topologically dies during topic doesn't mean that they will be coincidence and in general the further than they are often mysterious center the more likely they are to be coincidence and behave as if they are here we see them as well-defined peaks at very different positions there bold double of cortex that's said the here the Q we'll talk more about the splitting patterned after they're being split with 1 big general coupling of about 10 hurts 1 2 bond coupling and with 3 bizonal couplings 3 3 by couplings of about it's just an hour after last thing I want to show you 1 last stand out while we're on the concept of Nicole performance so here we have the molecule 3 metal to you what I want to point out to you is in 3 methanol methyl to you and all the 2 vessels are not the same the dire serious topic you can think of this a couple of ways 1 way is is to think about member the OH constitutes a Carroll said there and you can do a little thought experiment and say all vision replacing 1 of the methyl groups where the other methyl groups with a Jerome methyl group or the other ways just to think about but when you look at it you say or how many peaks that we see in the the 13 an hour 1 2 3 1 5 the 5 types of carbon because there are 5 known chemically equivalent carbon so if you look at the proton NMR solo confusing at 1st until you think about what's going on it's not hard to realize that this methyl groups that data to an oxygen gives rise to the stubble now we have 2 more Mathilde loops in the molecule In each of those methyl groups is next to a hydrogen each of those methyl groups appears as a dumb but the double it's a very close in other words we have a double act In we have another double latte and so it looks like the Triplette what's up well you can just you can discern it if you look carefully because it's not 1 3 1 2 children 1 but it it's confusing so it's 2 doublets but only tell you a secret This is a 300 megahertz spectrum remember I said the coupling constant is fixed and hurts the position is fixed in the year so my 2 doublets would look like this at 300 and what looked like a triplet if I went to 500 megahertz the 2 doublets would now separation I'd see a double and a government that would be 1 way do are I think that's what I want is safer today about chemical equivalents will pick up next time talking about the medical report


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