Lecture 14. Spin-Spin Coupling in Stereochemistry and Structure Determination

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Lecture 14. Spin-Spin Coupling in Stereochemistry and Structure Determination
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Lecture 14. Spin-Spin Coupling
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Nowick, James
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This is a graduate course in organic spectroscopy, focusing on modern methods used in structure determination of organic molecules. Topics include mass spectrometry; ultraviolet, chiroptical, infrared, and nuclear magnetic resonance spectroscopy.
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so when we were talking about coupling constants I said sometimes there's some really big differences between coupling constants distinct differences between coupling constant so I can l canes if you have a sister couple lying your J 3 HH is about 10 hurts if you have a trans coupling you're J 3 HH that's 3 bond coupling area personal coupling is about 17 herds and by the way I will again cautioned you to make sure you understand the difference between coupling through a double bonds versus coupling between double bonds so a lot of people particularly when they are Starting Out confused scarier chemistry we have confirmation you can rotate about single bonds so even if you have a bond between the 2 single bonds that might be s sister restaurants that's always a dynamic equilibrium that may be heavily weighted toward 1 way but that's not scary chemistry that's confirmation and that but mind you has a different Coppola's was curve then the cop was curve for a N S P 2 S P 2 carbon of it's connecting to hydrogen so anyway this is specifically not on here but let's not talk about cyclo hexane which is what I'm going to to choose for 2 days today's lecture and just remind us of some of the key features I pointed out previously we talked about the cop was curve for 3 sp 3 systems and we said that there are some very distinct relationships better better insightful hexane so 180 degrees gives you a big coupling constant 60 degree relationship gives you a small coupling constant sorrow axial axial coupling has 180 degree died he grow relationship those of you who are the previous staff class that was just filing out got to you handed talking about Newman projections of a few Newman projected you have a 180 degree died legal angle and typically you have a valid 210 herds for an axial axial coupling if you have an axial act Ecuador EO coupling these are of course all 3 Borland couplings Marina Vittorio Equatorial coupling you have a 60 degree die he galangal and you remember the cop with her very that grew out before and so that's about 2 3 hurts for each of those so what I'm going to do right now these pass out 8 work were mentioned a very real example that just came up in my lab and I thought it would make a cool cool example for suspected sister chemical problem associated with the conjugated additions to AT & alpha-beta unsaturated come so we were working with cycle scene the 9 per cycle heck scene is Electra fell like at the beta position and we were doing addition of adolescence are right that is pH in each think In addition product and so the issue here I was whether we have the transpire warrant assists Friday at the foot of the and so all of these 2 stereo isomers what we call the relationship between the stereo isomers serum or so all of these 2 dies immersed each of them of course is formed as the Rasim 8 and that doesn't matter because you can't tell 1 Indian Amir from another by an a modest spectrum of oversee make mixture is identical to the spectrum of either in individual in India unless you have some sort of coveralls solvent or unless I prepare a Cairo derivatives so the only way I could distinguish these 2 will part would be safe to make enamored of the 2 an anti-virus apart would be to make an where I had a car rolled acid brought into making and the word to use something like the kind of shift reagent or economists often engaged so the big question is which of these 2 is 4 persist for the assists were the trance In what appears set out the spectrum will take a lot and analyze it and I have a few extras here everyone else 1 more than here I'm great so we have here the In a more spectrum in chloroform solution and what I've done here is I've blown up this region the midfield regions we call this region the downfield region this real reason region the upfield region and I'll call this the field should felt molecule of course Is Night has a fennel group in it and so I think it's pretty obvious that our federal groups please over here you might notice for example if you look at the fennel group that we have something that looks like a double-edged for an apparent double that corresponds to the Ortho protons there may be some medic coupling going on there were not going to be talking in any great detail about this but I just want you to get in the habit of always reading your spectrum so that
corresponds to the worthwhile we see something that looks like a that's the same integral you notice the high in the integral from here to here is identical from the high from year to year so that Triplette were apparent Trap Triplette corresponds to the matter protons 2 of those and then we see something that looks like a triple it over here and again it's either a trip later apparent trip later the some small additional coupling
US H M In that corresponds to the paragraph 2 and I don't know if you can say on here but you certainly can see on yours do you notice where the author of Proton and the matter pro-Taliban up and India and the pair talent show up what's the chemical shift roughly 6 . 6 6 . 7 cent aromatics typically 7 do you know why they're upfield nitrogen donations of the electrons pushing in from residents off of the nitrogen by residents we get extra electron density at the Ortho position in the power position and so that ring is shifted a little bit upfield which is kind of cool if I made enamored out of that nitrogen which would pull electron density out these guys would studio over award field and hear this old guy over here this is your core right all of this is all of the others cyclo Hextall stuff that are not directly involved in them we have 3 peaks in the midfield regions remember right now we don't know stereo chemistry and we don't yet know what's what what we have repeat then they say so we have these 2 protons and the end something very interesting happened with this sample on this wasn't anything that I had planned on it was simply the day a day later I went to rerun the sample the same sample and the midfielder region looked a little bit different this is your day old they all charitable this is the freshly carrots and what's going on there so we still see it James said nitrogen is swamped with deuterium so we still see it but now it's brought what is that us maybe Maurice if it were very very wet this year's peak over here said this is and the sample was nicely sealed so this will be here at 1 point 6 is H 2 0 that's about where you see at 1 . 6 1 . 5 6 that's very typical for H 2 encore form so we don't have a lot of water in their pride about 10 20 mill Moeller water and we have lots and lots of samples and what else did I tell you about 4 of you can generate 8 and a little bit even a little bit that forms is going to cannibalized the acceleration the exchange of any dangers between molecules or between molecules in water so even if you form just a little bit 1 per cent for example plot I guess to be DC all but the majority of course Corsicans 1 per cent of Europe you know your molecule 1 mole per cent majority still 8 C all but what's happening is now your energies instead of saying attached to the same molecule are getting swapped between molecules and as a result in this case is also getting swamped with water but as a result of that Proton doesn't stick around while tens of milliseconds for hundreds of milliseconds you can't see the spin as to whether it's been up for spin down so we lose coupling it becomes a single in this case the broad England now let's look at these patterns here in the united on exchanged samples to these are all the midfield so which ones the teenage over here 3 . 4 relish the it is the end of it and so the other 2 and will talk more about this in a moment but the other 2 1 of them changes a little bit patterns visible art let's let's talk now about what we call these patents to whatever we call this pattern we saw last it's a Triplette of Douglas you have to be coupling constants and 1 small coupling what are we call this pattern here a quartet of doublets so you have roughly 1 2 3 2 3 2 1 ratio the rolled double its and if you wanted to be fussy about it you could say Well you know my quartet isn't quite perfect banking see these 2 are in quite the same as the ones old battered than the other you know because all 4 coupling constants may not be exactly the same but the the same within our efforts were half herds basically the within the line with the individualism so if you didn't like to analyze it is acutely you could call it an apparent Q I'm fine with you there I think either of these accurately reflects what you see and hear the views said it all I kind soreness Cielo humping thing over here and over there you could call it an apparent it's all right apparent unhappy with you there analysis on this or so and you'll notice this paper simplifies the quartet of doublets simplifies which makes sense because that must have been the proton that was coupled To the NH group because we lose that coupling so that courts had of doublets nail has become on apparent TD the what's not Terium remember even you're getting a minuscule amount of DC LME putting numbers this sample is 15 Moeller roughly we have maybe generated . 5 available reduce CO but that TCI was enough to catalog the exchange and this NH isn't sticking around on this molecule every millisecond
this NH is bumping into another molecule and trading partners or every millisecond this molecule is bumping into an age to a little bit of the H 2 0 in the sample and trading partners typically when I prepare a sample like this I pass the solvent through flame referring stride aluminum to remove traces of water and DCO 1st if I won and I spectrum were DMS OG 6 is another good solvent because its hydrogen bonds nicely and typically keeps Europe all wages in place by stabilizing them so carboxyl again acids that are hard to see in cough often show up well in India question what is your best so what and the water so the water could help the exchange but apparently not enough that it actually know that Proton actually does stay in place very nicely and just when you get some answers in the sample is 1 thing what is that really a single so we would call this a broad singlet B R s and so OK great question the QBE is becoming a TD and remember how we teetered on the edge here between being a triplet of doublets and you can kind of see a little bit of hope the stuff all the 3 jails aren't exactly alike they're all different sorts of protons with their own specific dying roles coupling to wed so there are some differences and so depending on the sharing of the instrument 1 day 1 time it looks like a TD and the other time this looks like the DDD with 2 vary very similar coupling constants so we can just at this point C 8 lines here and so at this point just due to chance of the shimmering were able to resolve the 2 coupling constants that differ by about a 3rd of becomes a did you do that's this is purely purely coincidence if I had this with slightly less good shimmying it would have worked exam alright what I want us to do now that we've thought about this a little bit is to extract the stairs chemistry from here so we buy figuring already actually happened to know then that this Proton here corresponds to this 1 this 1 here corresponds to that 1 but even if we did we'd be able to figure even if we didn't have this spectrum you'd be able to figure that out by the amount of splitting OK at this point I want us to focus on these lines I want us to extract the coupling constants in going to show you how wide and how I handle my own data had made things bigger on the back so this is a peak print out I'm a big fan you get this from a 2nd a separate command the spectrometer on the big fan of getting the speak print out because in addition to giving you the piquant frequency of each line in ppm it happens to give it to you and herds which of course you can calculate just by multiplying the spectrometer frequency but the other thing that's really useful is it also gives you the peak height so that if you have a little straight pizza if you have either an impurity hearing on first-order coupling in there you can pick out main here everything happens to be very very straightforward so that 1st multiplex the 1 that's the triplet of doublets has 6 lines to too wet and son just drawing a line with my pen the quartet of doublets has 8 lines to and the doubling of goblets it has 2 nights at the Dublin has streamlined to Alright Still remember analysis of 8 triplets of doublets we slept with a binge Intuit Triplette in other words we have 2 of the same big Jr and then we splayed each of those lines further into a double and so we get this 1 to Tudor ones pattern where the lines on the outside a relative height on the lines and inside and if I called my lines if I called my lines 1 and 2 3 4 5 6 then the distance of big coupling is 1 to 3 hits to the former it's three-to-five it's 46 but I 6 1 2 1 2 3 2 of the 4 3 2 5 6 is our big Jr In 1 2 2 0 3 to 4 In 5 to 6 is small jets and you can see that here so we're dealing with real data now when I showed you before was simulated data on all those lines were exactly the same distance apart because it was fake data because it was so now to get the most accurate value over Jay's remember you've got digital resolution you've got the fact that the 2 coupling constants may not be exactly identical but we can't extract them separately because we're not seeing separate lines Turns out on that later spectrum were you did see the pattern resolve into a D D D deep I was able to extract them you'll get practice we got practice with the DDD remember 1 2 2 4 and 7 to 8 is a small generator 1 2 3 and 6 2 6 2 8 is your medium judge and then 1 2 8 minus big jet medium James small today is revenge for DEA but here all we can do is extracted and analyzed what we say which is 1 big J In 1 little sold him to get the the most meaningful data out of here I'm going to take all of those numbers and average them so get sharper pain here because it's a lot of writing to do here so if I take the and I jotted it down normally you could do this with a calculator so I've jotted down here the 1 2 3 is 12 .period 2 0 8 2 0 the these 2 to 4 it is I'm sorry it's 10 . 2 8 2 the Tudor for is 10 . 2 5 3 the 8 the redefined is 11 . 1 5 and the 46 is 11 . 2 8 0 and those who are vague J. values so what I'm gonna do is average them Of all of that of all the 1 2 3 dutiful a 3 2 5
and 4 to 6 and I got the average is 10 . 7 hurts you know I take 1 2 2 1 3 2 4 2 and so forth In the average of those he is well let me get the numbers 4 . 0 6 5 4 . 0 3 6 4 . 1 6 so the average of those years 4 . 1 hurts or so if we wanted to report this speak the way I would report this peak the tabulated to give us the short story is 4 . 3 8 I call at 8 TDD or an apparent today maybe because I'm seeing that there is some deviation here I might call an apparent T DJ equals come their J equals 10 . 7 he and 4 . 1 and I didn't go do the integral here but if I did the integral I mean I did it but not nailed it was be 1 hydrogen but the question to this point yeah I take the I'd take the average of it I want to show you something I like to do I like to take it the print out and throw it into a spreadsheet you will find on on most of the problems that I have assigned actually have a digital version that you can highlight with your cursor pace or whatever spreadsheet program you use this 1 happened to have been done a while ago and so I didn't doubt didn't do that but it's very easy if you can
slap the the date in spreadsheet even if you can't I'm a huge fan of the CIS somebody help me out here because if I make a mistake normally I proofread I'll just 11 . 8 7 . 9 to 1 and you'll see how quick and easy offices 11 . 8 3 1183 . 6 3 . 6 8 0 11 . 7 7 1177 . 7 7 4 the my doing right 1177 . 11 73 .period by the way number pads are also extremely useful on this 1167 . 305 for data entry but again I made a big fan of pasting stuff in and you definitely want to check your data because the literature is just full of crappy errors in data and you do not want to be contributing garbage to the literature where to put in more concrete terms you don't want your committee going in handing you back your 2nd year report with the non passing review but because you've contributed OK so I think I have all of our numbers there OK so this is a quartet of doublets so it's going to be 1 minus 4 1 minus 3 and it's also going to be to minus 4 3 minus 5 4 minus 6 5 minus 7 and 6 minus 8 so I can get all those values and I can just take the average can I get 10 . 3 so that's our big J and a small is 1 minus 2 however In the
end it is 3 minus 4 indeed is 4 minus 6 therefore minded 3 minus 4 5 minus 6 and 7 my and I can again just take my average against I haven't done pasted all the way down an obvious what the evidence is there arts and the average there is 4 . 1 itself I can go ahead and transcribed my analysis over and
course normally I would be sitting
at my desk probably with spectrum in front of me or my group members would be sitting sitting at their desk so the next 1 week and described as a 3 . 9 0 Q did heir-apparent Cudi if you prefer 10 . 3 cents it really did look like that analysis was completely on I'd call at 10 . 3 4 .period of equals 10 . 3 4 . 2 parts 1 h In usually from being good particularly with Mike computer I will separated numbers from units so I will separated ah but a space in here put a space in there because you separate numbers from units in the space here space here and the last 1 I didn't do it but it's a double at its 3 . 4 1 and it's indeed it's just the difference between these 2 lines which happens to be 9 . 5 hertz and that ends up integrating into 1 Our thoughts and questions but I drove next between the 2 1 let's let's find out so now we've extracted our data now it's time for us to analyze the data and figure out hysteria chemistry of the the molecule and also to think if there are any any conformational issues so generally when you have a problem where there are 2 possible answers the best way to approach it is to go ahead into try 1 answer CEO fits try the other answered the outfits and see if you can distinguish them apart so I'm going to to go ahead and drawn a cycle hexane ratings and let's start with the trend scarier license and if we have the trend stereo isomer I'd assume that a favorable from would have the 2 substituent In the equatorial possession now I wanna known this Apple your in terms of the confirmation of the meeting but that enraged couplings pretty big Dublin with 7 with 9 . 5 hertz that's consistent with the party playing a confirmation remember that's not terror chemistry that's confirmation but I can be pretty darn sure that it's real estate to draw like this so I think that I know right now Is this is our double it with J. equals 9 . 5 if we have this molecule this Proton here how many big couplings would we expect to it and how many small couples we expect Q To entered Perry planar couplings so we have this axial protons giving an axial axial coupling to this 1 an axial axial coupling to this 1 and so OK and 1 axial Ecuador Orioles so we would expect it to be something akin to a triplet of doublets with the day of the trip with the big Jim about 10 in the little J of about 3 and so what we say here is actually a team the core apparent TV With J. equals 10 . 7 and 4 . 1 parts those of the data that we extract and that seems seems so far the pretty wins on what would we expect for this Proton somebody else 3 axial couplings so we would expect and again we wouldn't have priori know whether I'd expect the big coupling on small coupling or no coupling at all to this NH aged depends on the confirmation of you draw the fennel matching makes a hell of a lot of sense that it sticks out like this on the island of words that it really does push it in the Perry plainer but happily Orient might not know what to expect but it expected lease a big coupling From this guide to this guy axial axial and at least the big coupling from the sky To this guy and we know from the J of the NIH said we stand as fresh spectrum fresh sample where big there so what other couplings what we expect 1 axial Ecuador self this 1 here we would expect to see as something like a Q & a on apparent cured and we expect to have 3 big couplings and what we see is J-PAL's 10 .period story 4 . 2 now coupling should be mutual and coupling is mutual but as I said You're aligned with digital resolution Eucha about a hurts Digital resolutions actually a few tens of hours line with his pride about about 1 . 2 hurts but within the limits of the digital resolution and more importantly the line with were not getting a separate splitting here ditto over here we see 10 . 7 which within the limits of experiment is the same here in fact you could say that we were kind of teetering on the edge between that opportunity and a d typo seeing some of our additional splitting because you could see all those what spacings warranty equal but we couldn't resolve it any better on so we see a Q Darren apparent acutely with 10 . 4 2 and this is what I report and it's consistent with the state but now we also need to think this is super super important because think about this you start on a total synthesis of a natural product you do a key step that gives you stare chemistry early on in the synthesis and you make a wrong conclusion and now 20 steps later you finally get your natural product except it doesn't match the published new trouble the new ready to graduate and you find out that you're you're synthesis of isn't going to be titled total synthesis of hard complex molecule but rather totals this is of at hard complex molecule and that's not nearly as good so this is really important to get us OK let's take a look here so a mansion for a moment that instead of having the molecule as the train stereo isomer we had the molecule as this history and I don't know with the nitro groups going to want to be and sealed off the Niger groups going to 1 of the equatorial or from going to expect some confrontational mixture rapidly equilibrating but let's start with the premise that the maybe it would be axial and let's think things through I think it's pretty reasonable to assume that the trail is all like widows both Ecuador El Dai Ecuador railcars died axial would be during flat that have to be some situations axial but here we have a nitro group can win group the both so what would we expected that for this Proton Alpha to and a nitro group Balfour to an excellent 3 Equatorial couplings so what would you what would you expect that to be like a quartet with what sort of J something like 3 Xu al-Sayegh might be an apparent Q something that looks like a Q J. equals I'll say approximately will most likely 3 her so that would be a prediction for this 3 Equatorial L axial of Equatorial equatorial about 3 hurts Equatorial axial about 3 herds Equatorial axial about 3 the hears the cool thing let's suppose you couldn't even resolve the multiple let's oppose the multiple it was a little broaden the shape you could look at them multiply and say so let's say for a moment that Multiplex what I would be given a low-cost options let things let's suppose are multiple it looks communities where back I right not pretty like a snake that it swallowed an elephant or you can go ahead and say I can't get a peek print out on this thing but I can measure this distance with my 1st serve if that distance looks like it's about 12 per that sure as heck is not consistent with this 1 here because this 1 even if you could resolve even if you couldn't exactly take it out what would that distance the about about 25 per cent because we'd expected to be tender so plus 10 years so plus 3 or 4 ourselves so in other words using the number 10 Hertz which was just sort of a number I wrote on the blackboard of 800 tonight hurts I would expect it to be at least 10 plus 10 plus 3 2 big couplings of about 10 hurts each and 1 will coupling about 3 hours to so that molecule could even if it didn't give me it's coupling constants precisely would scream at me that it was consistent with this another consist now what would we expect to see for this Proton here let's assume that we continue to have coupling to disseminate it's about 10 per what would we expect to see here you to die axial couplings Sauer are right good so we would expect to see it as How would you describe that pass the triplet of where TO UT or something that looked a heck of a lot like it or not don't like calling this an axial coupling has that special I mean it happens that we happen to have a big here but it's not really axial 1 here .period think about it because it's not honoring its axial right but we see it's space anyway the point is you would have 1 big coupling on the cycle of hexane ring 1 coupling to the NIH that in this case we happen to know was about the same size and into small cup consumer pattern would look like 1 2 1 Chu for their 2 0 2 what the what the on the whole he said that the next you are so they they couldn't so great question so the question for example is why do they not Split differently and the answer is they displayed different were the same if the guy he galangal is similar then you will see the the same Avery close the same if the he galangal is different see different it may be a and we saw how this was teetering with the spectrum were coupling constants that were the same within about efforts were quite resolving apart 11 and 10 9 . 5 and 10 . 3 so it might be that this pattern instead of being HQ could be a 2 a day or a D 2 year warranty deed did with 3 small days for example it could be a DDD dealing with 4 3 2 and that would be consistent with the Saudi dealing with 3 2 DT with 2 wins 3 or 4 free and that would be consistent so 3 small Jason there are a lot of play with this idea for a moment longer and the question what would happen if my assumption about the animal in Group B in the equatorial was wrong or is incomplete and sold during flat isn't the managing for a moment that my Allen group is axial In my nitro group fears Ecuador and so if we had this controversy the use of both we have 2 different controversy here that were considering so let's take a proton Alpha to the 900 what would we expect for this Proton now In this confirmation of persist during 1 axial so it's this 1 to this 1 and to Ecuador oil partners so 1 axial axial coupling In 2 axial Equatorial coupling so how would we describe this Proton here a double-edged of let's Dean teeing were apparent dt and what would we expect suggested 1st name for the coupling constant that for the multiplex is double that so that's the big splat 10 something at 3 4 or something something like that so we would expect it splash with a big J In splits into a Triple-A with roughly a small and so the pattern you'd see is something like 1 2 1 1 2 1 With this distance here being 3 3 3 3 this guy here and let's assume again that we still have a big coupling the animal so the 1 itself to the nitrogen here what we expect for him to a large so I'm assuming were lodged to the nitrogen that's kind of a wild card and then Hauritz coupling partners that axial so this is axial like withdrawal this is is Equatorial Ecuador this 1 fax so what we used to we have unassuming were big jaded the nitrogen let's assume let us assume because we happen to see that that NH was flat so I'm assuming that's a big J. water all over other jails not all small so so this 1 we would expect to see as a D as a DQ or parent DQ depending on how it is and this 1 we would expect to see the big J 3 and the small that big Jake 10 and small Jafar Art last thing I want to do Our let's call this Siskind In this system too now a mentioned that we had an equilibrium which you may worry well a conformational equilibrium there to make substantial and between Siskel on 1 insists confirm or 2 and I had equilibrium is going to be wrapped because ring on a cycle hexane as and I just want us to think now about 1 of these protons let's just talk about what we would see for the proton its Alpha to the nite drew group which I'm going to call 8 7 this is what I want us to think about is it scuffling specifically with proton beams of protons see and process Sunday will call B and C the ones that are on the methylene group but the back the the 1 that's on the mat on the front and still be is axial Ecuador a here and this is Jane and what I want us to do is think about what we would observe if we had a dynamic equilibrium between kind former 1 income from her to what would we expect so if we lock as JCB income from her number 1 it's about 3 hurts because it is an equatorial Ecuador EO couple if we look at singing it's also about 3 hearts because it is and Ecuador axial coupling and if we look at J. A D is also about 3 her and that's why we said that Proton was a quartet income from her number 2 if we look at it JAG now is very different it's about 10 her because ABC His axial axial is axial like with Orioles so it's still about 3 hearts indeed His axial Ecuador e-mail so it's about 3 her so now we we somewhere the middle here not all come from the White not all come from a 2 we would now expect to see 1 coupling constant that somewhere between 3 In 10 hearts and 2 coupling constants that are both about 3 her so we would now expect to see this as a deity parity today or something that showed To be 1 big coupling and 2 small couplings in other words a big all of 3 detained herds if it were right in the middle we'd say about 7 hurt so that might be my 1st guest and adjacent mall all of about 3 hurts so regardless of whether we had the CIS as 1 conference the as the other come from or the CIS is a dynamic equilibrium in which both controversy president are observed data out of a triplet of doublets with 10 . 7 and 4 . 1 hurts strongly matches the trams and does not match the so that gives us the economists are right we will pick up next time talking about other aspects of structure in in Amara and specifically where guests will talk about coupling involved in other nuclei


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