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Lecture 17. NMR Spectroscopy

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and so the president of the United States just announced a major new scientific initiative kind of on the scale of the human genome project of which were has been so far the largest initiative and greatest scientific achievement in my lifetime is to see the human genome sequence and a new initiative is going to divert huge resources but from the scientific community to this important project the goal is to map the human brain to back the function of the human brain pathways within the human brain pathways that lead to diseases like schizophrenia depression and memory or something the house climbers and so that's the goal the goal is ultimately to create some sort of a map like this on that allows us to see the pathways that lead to diseases or make people smarter for having effects like that of so that as I looked at all the news articles that were pouring out about this it made me wonder what take to see inside the the brain but ultimately the picture there is developed will come from different new imaging methods that allow you to see inside the brain and probably a lot of modeling computer modeling those pieces of information together and sold stock about what it would take to look inside the the human body and see something going on and so I
thought I'd put together a just 1 diagram pictured LPC wouldn't mean see inside of tissue supported you wanted to see inside my arm you couldn't see inside my mom all you see skin and flesh and that's because the might my skin is not transparent to light the the light bounces right off is reflected in the UK and see what's going on inside and so if you look at it at the different types of spectroscopy that we talking about in this class USA was also injured in Kenwyne 1 General Chemistry you spent a great deal of time in General Chemistry using you need spectroscopy that these would be years albeit law still applies the IRA and other types spectroscopy which abuts solutions and little cadets and measured how much like that was absorbed that I stretch out the electromagnetic spectrum and this is just a small fraction of the electromagnetic spectrum or you can see the starting down here at about 200 to 800 that's where you did you read this spectroscopy as and as a freshman taking some sort of a first-year chemistry class and there's a lot of stuff that absorbs you never get any spectroscopy and EU leaders below 200 because even water it's pretty strongly there you were typically doing need spectroscopy in this region where you can see organic compounds so water absorbs strongly there were not going to see anything in the brain below 200 million litres of water would simply absorb all the lights from 200 to 800 million liters that you need his you still can't use like very effectively a little bit but not very effectively to see inside the break so the 1st problem is your skin contains material called melon and that is very good at absorbing life like never passes through my skin that's the purpose of the melanin in the skin that's what makes skin as around issues associated with it's all that's known absorbs light very effectively at every single wavelength pretty much on and even if you stripped off my skin or stuck some sort of probe underneath my skin the problem is that there's blood in there and blood contained globally that's probably the most prominent "quotation mark crumble for you at some wavelengths is much more strongly absorbing and others and of course that's ready and it's strong absorber and see a lot of blood also prevent you from visualizing we also talked in this class of higher spectroscopy way out over here and you notice about 2 I'm using 2 different units you need this spectroscopy using manages to measure wavelength and might recall the measure of high art sector using frequency using on using this inverse cm wave numbers types of units and I kind of glided with those units here since the other fits in with you spectroscopy and all kinds of stuff especially water absorbs in this region that might never take our spectra in what we never use water as a solid Fryer spectroscopy because it would absorb too much like on but down here in this region between you believe it In between Irish spectroscopy this is called a near IR region and if you look here in this little valley this region right here is the most traders appeared region of the spectrum typical organic compounds don't have soared in that region and so if you could design a small-molecule probes that absorb you could see where there is way those probes are inside the human body if you were a jellyfish sorry if you were if you had some sort of special viewing ability and you could see in this region that has the best transparency where few things absorb if you could see it at those wavelengths I would look like a jellyfish to you I would be transparent delay would pass inside to go right through me could stand on the other side so canister are actively now trying to design organic molecules that absorb light effectively in this region because you could use those as probes and tags to put inside the brain to put inside the body and watch where they're going and the like will pass right through the right through human tissue very effectively OK so long so this was during your 1st year of General Chemistry in our 29 higher spectroscopy and now it's only when to switch gears to talk about a completely different type of spectroscopy last but
the thing that question that before
long the government has turned down the hall or what actually that was interested in listening to more Munich monitoring this is an animal so when I was a graduate student and I use in a modest Almeria who that's going to continue installs run March commentary with little speaker on selected human molecules each time and I'll explain what that little post was about and just momentarily so I apologize for the volume on the middle of wake up this morning but gave up so Chapter 14 were starting a new type of spectroscopy we spend a little time talking about spectrometry and then we spent a whole lecture talking about our spectroscopy and hopefully you've been working all problems in the chapter on higher spectroscopy and I'm going to talk about nuclear magnetic resonance spectroscopy that the fundamental idea is the basis for MRI imaging for magnetic resonance imaging underwater nuclear senior has nothing to do with both with nuclear power radiation the kinds of radiation that comes from nuclear power plants and nuclear bombs on this is that this is based on radio frequency energy because I wanna start by talk about what are we going to see if we use nuclear magnetic resonance spectroscopy and when you see you are added in a specific property of Adams and let's talk about what's required in all areas to be able to see things with an enema spectrometry there is a fundamental requirement of the Bills Adams must have a property called nuclear spin and that's not a particularly property of elements it is a particular property of isotopes so if I take an individual elements such as well the hydrogen atoms there's multiple different isotopes used protons there's deuterium and tritium and they're not all visible light and I'm not so in order to be visible light Panama but you have to have a property called spin a particular isotope has another property called spinning making got speed there is a quantum number associated with you of on and so in order to see things elements by immodesty isotopes in March you have to have a non-zero spin quantum number and still more urgent that spin is because a spinning wheel places like a tiny magnets and show it has magnetic properties when you put 2 nuclei that together those 2 tiny magnets can interact when you put its nucleus with spin In a big magnetic field that will interact with the magnetic field so if we look at the common isotopes on organic molecules carbon hydrogen nitrogen oxygen yes moved but I wouldn't call them diet magnetic media pair magnetic would be a better I'm not even sure not enough of a physicist to answer whether Perry magnetism is a good description of a nucleus but it would be dyed pink diamond that's for sure OK so but so prone the typical ages you see attached to organic molecules those do have nuclear spin and there's a specific spin quantum numbers associated with associated with that one-half totally inconsequential to you don't need to worry about what the spin quantum numbers for Proton and most of the pages see attached to carbon 99 . 9 8 per cent of ages attached to carbon atoms your body in biology it the the floor everywhere it those are protons or with a with this with no neutron nuclear so various easily see those by and so that's the most common form of today His Proton-M and that we're seeing now is a very small fraction of the features that are attached to the to the molecules in your body or deuterium that 1 extra neutron in nucleus chemically behave exactly like protons all the reactions see switched approach on the nuclear reactions would work in the same way on so the problem is that deuterium is not very abundant and so because it is not very abundant you could see them by an or jacked up the power Indiana Minamata see that tiny amounts of deuterium there but it's very frequency generally you don't worry about seeing deuterium by animal you could if you wanted OK ,comma you can't see the most common isotope of carbon carbon 12 so if I look at all the organic molecules in the body glucose on glycerol the high street past glucose 6 phosphate citric acid most of the carpenter totally invisible by and more you can see them by an remarked that the nuclear I don't have this property of spin on but there is an isotope of carbon that you can see by animal that does have carbon 13 and the problem there once again although not to the extent extended deuterium is that it's not quite as abundant the only 1 out of every 100 is a C 30 already carbon 12 they react the same all the same reaction you can't distinguish them by doing some kind of chemistry on and so you can do and Maurits not as sensitive to checks here Proton because it's so sensitive the kindergarten and markedly better again jack up the power in order to see the tiny amounts of carbon that are there because on average so few carbons are actually season and all these other elements that for August is only 2 other ones that principal importance of oxygen 16 on and nitrogen that those are not an 14 those are not in a more active so we're not going to look at oxygen you couldn't even see them you can see the oxygen and nitrogen is on molecules grandma always going here carbon and hydrogen so for the next 2 3 lectures rode atop a Proton and mind carbon among those are types and why that will be that are useful to chemists the that following sorry I thank you for clarifying the identical to scratch there's a nitrogen invisible oxygen invisible even if the you get 50 oxygen than a molecule totally invisible landmark OK I shown picture here and not spectrometry was in the basement over here right always got a huge rooms of 3 being the US spectrometers much larger than this 1 this is a smaller spectrometer and inside of this respect from 1st basically a big tank inside the tank there is liquid nitrogen 6 really told us the Member temptress employing minus 200 degrees inside liquid nitrogen there is liquid helium 4 degrees Kelvin and liquid helium is
used to cool down the superconducting copper coils right there that's a bundle of copper wire and the start this electricity manager that world copper wire and then take the electricity way and because it's it's so cold the copper superconducting and the electrons will flow instantly In that in that around to creating a superconducting magnetic field so when every half of current running through a coiled wire creates a magnetic field and I've drawn the magnetic field lines for you here as you can get a sense that went through the center of the and you got this Super Duper Dupre massive magnetic field over each of our demands we got his planters out in the in the area between the buildings so you don't drive your car over there enlisted the field a walkover that your pacemaker and end up dying so if you want to work for a man wearing economics are the right below those planters in front of minus hole OK so that more spectrometry and normally they're not cut open the skies unnatural white at that opening must be broken in some way so I brought you a picture of an attitude with animosity standpoint this is so this is the way we put our samples inside that Panama magnet men and you can see here there's a little bit of liquidity here and it's gotta do rates on there and we dropped that sample down the center of sits on a cushion of air the keeps right in the center where the magnetic field is powerful so that's the way we do and what we you dissolve some of your sample if you put it in tube you drop down the center of the Panama magnet and then it's sits there in the magnetic field in and you can't you just any old solvents to Anaheim and I don't know if you can see it is because not focus very well we we have special solvents and with this so I can't even see this is focused but if I try to focus on the bottle which appealed to read here is that this is of there's no protons on this is chloroform C H C L 3 but they've taken off the Asian economic material you don't wanna put a solvent with protons in online and there Of all the protons in the solvent Of all the signal so we used due to rated solvents with deuterium is for an almost exclusively OK so that is standing on the big magnets so somebody that's how much the costs depends on you novel excited by how much does the car cost tens and what car you buy and generally it's the size of the magnetic field that makes all the difference they can cost anywhere from 100 thousand dollars for a superconducting from 2 to 2 million dollars depending on the size so we have a multimillionaire mom over on the side of Natural Sciences 1 but that's vastly bigger than the ones we have over here in around that's used for for looking at things like proteins but this was going on inside that deep inside that and when you drop your sampling yeah OK so you drop your sample inside of that an Ahmed decision massive massive magnetic field and you need a massive magnetic field it's absolutely essential for the experiment so inside that supermassive magnetic field .period so let's just imagine that we have this super massive magnetic field and symbolizing that this shady hero here labeled NMR magnetic field so surrounding air molecules on Bolton on every side of the city super powerful magnetic field and I already told you that a proton is like a tiny magnets that Proton knows 1 of 2 things is either aligned with the magnetic field or doesn't miss aligned with the magnetic field those 2 distinct choices and they are quantized choices it doesn't matter if they're sideways and laughter right there's 2 choices aligned or not and 1 of those is better than the other it is better to be aligned with the magnetic field and Aldus right aligned with if you're in line with the magnetic field you're happy as well as the tiny little proton manner that's a good state to be in and energetically stable state but the alternative is that you can be aligned against the magnetic field and this is where Qantas of states is so mind-bending it's what happens if the halfway line manager who go there right it's quantized your aligned with aligned against and those are the only 2 choices and the more powerful your magnetic field is more stock closed 2 choices are so we need to always try to have the most powerful magnetic fields possible so there's a good state stable aligned with the field and then there's this other state that is not a stable the tiring energy we're aligned against the magnetic field and the point is that you can transition between these 2 things with energy so in other words if you absorb a photon at just the right energy so if he is able to with just the right engine you can flip the spin so its missile so it's aligned against the magnetic field if you had just the right energy it is perfectly matched if you put in the wrong energy will flip that spin and that Proton will sit there and sit there there eventually it'll jostle around for the molecules that eventually will spontaneously revert back to the others can see and when it does when it does that it will the energy at exactly the same frequency that absorbed manager and this is the basis of the earmarks fare well at the beginning of electric played for you this sound and I don't know if I can go back to that ultra take this thing off the screen for a moment you can hear the sound in all its glory again you're listening to an Panama experiment what's happening is the animosity ,comma pulses disabled and then them spectrometry listed and it's listening for all protons in the sample the start getting back their energies at their particular frequencies so let's listen to all collection of molecules getting that managers like up in listening to protons giving that frequency Tom trick you don't hear the spectrometer 1 pulses because crew found out they would definitely competent listening to the protons adding that something if a triumph of some personal notices beads there on the that's a function of having 2 different frequencies and interfering with each other means is that the 2 peaks in that and more spectrum to frequencies that you hear in interfering with over
so that's memoir
experiment we drop a tube in his back ,comma repulsive energy the spectrometry listens to the frequencies and then foxholes frequencies for question the but when you pulsed with energy in every possible way of life at the same time you know became just falls with 1 frequency toss with this loud sound and that's exciting every single
possible frequency and then the protons all start admitting that spontaneously admitting backers look OK so here's here's a plot of frequencies there's a plot of nuclei and frequency if I had some organic molecule in I had just drawn at random organic molecule here this is to colorings on there I'm so that you would apply all the protons and all the carbon is getting back their energy to radiofrequency energy on 1 plot it would be the most useless plot the universe and that is because protons it absorb and emit energy in a completely different regions of the radio frequency spectrum from carbon in order to fit all that someone planted and you'd have to scrunch down all the proton peaks so small that you couldn't even distinguish them and the same thing with carbon except worse with carbon because the companies are there so few problems that the signals aren't very big so nobody ever plots carbons and protons in the spectrum we always do those separately we run our we blast with radiofrequency energy over here and then listen over here and then plot over here to see protons and we were interested in Connemara we blast with energy over here and then we listen we just plot this region individual so from now on I'm going to separate proton NMR from carbon animal we do those as 2 separate experiments because you just can't fit those onto the same plot so and it and so for the rest these lectures on Buddhist separately discussed see 13 carbon 13 along Proton mark but even on the basis of the experiment pulse with energy and lessen the basis of that experiment is the same no difference OK I want to come back to this this thing that I kind of feel just a moment ago that Panama's what about the physical and what instruments because there's an important point that I meant to make and realizing that I forgot it's essential for your understanding of why spectra look have all these years labels on them so here's our animosity drama that should be just a moment ago that seems the point that I want to make is when you order a brand new shiny Amaya paid 200 300 thousand dollars a year MRI it's just come from the factory that just finished wrapping all the coils and packing it up and fill it with liquid helium and liquid nitrogen on the problem is that nobody really knows exactly what what that magnetic field strength is going to be until they the man and that's the point when they 1st booted up that they realize all now we can finally measures this that the magnetic field of this custom-built superconducting magnet that we've created and no 2 animosity traumas had exactly the same magnetic field and that's the problem it is a problem that no 2 magnets know to big a 200 thousand dollar magnets even if they that the manufacturers feel like they in exactly the same way for that exactly the same magnetic field and let's see how that creates complications for the NMR experiments and how the community has had to deal with them and why you're never going to see is a structure that uses frequency for the x-axis yes so the question is and what is the reason why spectrometers don't have exactly the same frequency I'm sure it's an engineering issue and that not competent to comment on the higher they can't make them exactly the same that OK so let me give you an example of a sample this is chloral Assadullah right here and let's imagine I go to my lab I am sure we have Clairol acid my lad if I make up some simple and Panama to an eye-popping you expect from the on and let's suppose this is just thinking experiment that my spectrometer is operating with a magnet with a 9 . 4 Tesla magnetic field and I asked my friend I like all over the Hamburg Germany and I said Hey could you provide a sample over there in Germany of course that Allied and dropping your spectrometer the problem is they won't have exactly the same spectrometry maybe there's ,comma is operating with a magnetic field strength of 10 . 3 tests and it is it becomes a problem if our and mandates don't have exactly the same field trip because if they don't have exactly the same field strength ,comma molecules will not resonate will not absorb and emit energy at the same frequency so we won't get the same spectral so for example Tetra methyl cyanide and this is very commonly used in an hour spectroscopy ,comma will have a different of absorption and emission frequency Michael acetaldehyde the 2 cardinals in there I might see that absorbing 100 million 3 thousand 800 hurts when my friend in Germany will see that same carbon over here absorbing emitting at 100 thousand 571 in whatever 100 million and a different frequency is the port for all our frequencies will be different now how are we going to publish our data and have any 2 people tell that they made the same molecules and so here's what we do is what the community has decided to do to to make all this work what decided to do is we decided to have everybody measure their frequencies relative to 1 molecule that's this molecule Tetra methyl silence is volatile so he attitude lobster sample when you evaporate off the solvent detection of silent comes off the chemical she said that the frequency at which is absorbed and mixture is and isn't much lower than the frequencies for for most other molecules so almost always all the other peaks will be on the left-hand side here of the Tatra methyl silent and you're not seeing the silicon I'm sorry you're actually seeing the carbon but I need to point out now here's the important point if I got a magnet that's 10 % stronger in Hamburg in Irvine but all the frequencies will be 10 per cent larger so if I can just divide by that 110 per cent to normalize things that could just squeeze that spectrum stretch the other spectrum everything will overlay perfectly if you adjust for the magnetic field strength everything will really perfect so we don't plot spectrum In hurts infrequency what we plot is in parts per million everybody has agreed that they're going to squeeze stretch their spectra and plot out the frequencies in 571 thousand parts out of every 100 million parts of the so we list frequency using a simple symbol Delta and our units will depart for millions not say that if you wanted you could confirm the factor hurts at wouldn't help you or anybody else so we're never going to see perks on the bottom axis would we use this sort of normalized version of frequency and that's what allows regardless of the year and 1 anywhere on the planet as long as you take into account everybody's going to end up with the same spectrum everything is always measured relative to detrimental side Lane here's the cartons that's the carbon atoms there's attention awful styling that little peak here that carbon atom doesn't matter whether it's whether Tomba Irvine a Boston that's going to be absorbing emitting it at 48 . 4 million Nova here the carbon 194 up parts for million that's the cardinal Carter OK so we're not going to see perch within see part of this a 2nd features here because because the truth the spectroscopy is related to magnetic fields and that is we had special labels to our spectra and on we describe this region over here and you don't need to worry about what we describe this region over here at spectrum as downfield because in the old days plot
against frequency they plotted against changing magnetic field and you don't need to worry about why that is it's just going to seem completely weird to you that I'm going to sometimes say and I'm going to try to avoid but I'm to slip I'm sometimes going to say that carbon resonance downfield over there and you're going to say all down over now it's backwards it's Pat and I hang back and it's going to screw you up because when I say downfield mean hypoxic familiar I didn't invent the sorry OK so downfield when you numeracy downfield I mean high parts per million the other terminal use for this that this region of the spectrum is all to that is shielded and I'll explain that later OK so high particle million that's when I say downfield over here at this this region of the spectrum at higher frequencies from we are going to refer to this as upfield with low parts per million I have determined that the term that I'm going to use for this this parts per million chemical shift this is a terrible thing From physicists who 1st realized that there was chemical information and these frequencies you hear from me everything is chemicals that doesn't make sense to refer to this as chemical ship the physicist who 1st observed differences in carbon frequencies of proton treatment is what totally mystified at some share its chemical effect on so I'll still offered is chemical ship and this this region down here parts for millions of all sometimes referred to as the shielded and unfortunately it's it takes quite a bit of time to get used to those terms because the opposite OK so we thought chemical shift In parts per million will find some free and going to refer to 2 are x-axis chemical shift it's measured in parts per million and when I don't have space and the singled Delta that sort of try to avoid this this phrase downfield because I know it's so counterintuitive and upfield but if I slip you're going to have to quickly process in your mind with that means following words Our as a matter of manufacture mice so my intention was to draw 2 spectra for you and I think did applied in such a light gray United see with the naked this is this is up to minimize spectra of this molecule all of this died Romo propane you could have made a statement from the molecule here by just make sure that this focus and you could have made this diagram appropriate multilateral mandating a double bond doesn't matter how you got it if I put this into a little sample to drop Indiana in Maastricht ,comma and take a seat at the spectrum it will beautifully simple and satisfying the street carbons enable propane when I look at my my carbon 13 spectrum here it is here's my chemical shift to it's measured in part from million Delta Aussie exactly 3 all that's wonderful it's simple it's easy it's a fight fight which suspect ,comma type a new command and is the commentary OK now show me the the Proton-M more spectrum what also will be all will be unfortunately unmasks the last of the looks like this some other piece here and some other people here you have so many pieces there will be 16 peaks in the proton and more spectrum for this molecule 16 by how you get 16 pigs but there's not even 16 protons in here there's only 6 protons look at the molecular formula proton NMR is vastly complex related to carbon animal there's no one-to-one correspondence between the number of peaks that you see and the number of protons in a sample carbonara simple because there is a one-to-one correspondence between types of protons and private residences so I'm going to put skip ahead in chapter and I'm going to start explaining carbon and Margie because it is simple and powerful for you and then we're going without will talk about the complex that will talk about why there's so many peaks in the Proton and more spectrum so once you used Proton marker couple of years you'll love the complexity of proton because it gives you extra information when you're sitting down 2 years even it is say that sucks that complexity stocks right complexity and because you haven't yet spent 2 years looking at spectra yes well and when I put sample inside of that 2 I'm putting close to 6 . 0 2 times 10 to the 20 3rd molecules of greatness but you're not putting just 1 molecule to your putting and the resilience of molecules so there's lots of carbon atoms and there is no way to measure spectroscopy in a single molecule although the amount of stuff like you know drop of sampling and Marty it is is zillions of molecules OK so well and so the 1st and most powerful thing that you can do we're trying to analyze a mastectomy the most powerful thing that you can do this is to try to gage how many different signals should I expect to see In my car thirties spectrum but this is the simplest way to detail how does my spectrum match this structure or my structure match the specter of the simplest and most powerful thing you can do is to try to figure out ahead of time what once I look at the structure of any signals to expect to see and so the fundamental here Is that carbons chemically equivalent due to symmetry give 1 piece it's let's talk about the effect of symmetry in other words if 2 carbon atoms experience exactly the same environment and chemically equivalent if they would react chemically in the same way that we should expect them to do to absorb and emit a radio frequency energy in the same way so well let's start off as an example of of what what we're going to do will exercise where we try to guess how how many carbon peaks we should expect to see NSC 13 spectrum so I'm going to start over here and want to label these provinces carbon 1 is governed to His Coventry gears carbon for and I can immediately tell all 4 of those problems arguing distinctive carbon 1 is closest to oxygen carbon to is 1 carbon away from oxygen carbon 3 the 2 carbons separated from Archon controllers at the other end of the month all 4 of those are unique carbon atoms that experience different environments and couldn't possibly experience the same environment because they're separated by different numbers of bonds from that electronic of oxygen and I would expect to see for peaks in the car 13 and March spectrum for that I C distinctive cards that help you understand the issue of symmetry let's take a look at this summer of you know this instead of an appropriate sorry instead of in Eugene Ore here is turned Putin off and when I look at this see of carbon in the center here this Quaternary Cardinal called carbon won the Knesset carbon sticking up its carbon to the next 1 ,comma away from the oxygen and others to other carbon atoms here and those 2 other carbon atoms for exactly like carbon too if I just did it gave us a quick flip around carbon-oxygen bonds although the carbon atoms it's meant to be like a rotation there if I spun around the carbon-oxygen violent or whatever I would find is
that all of these other problems will be exactly the same as carbon to I'm going label carbon too indistinguishable there's no chemical reaction on the planet that would react if in a different way there related by symmetry there's is no need in principle you can use will allow you to name those differently and so is the carbon 13 in a March that for this I would expect to see only 2 peaks I would expect to see a peak for the carbon directly attached to oxygen and then other 3 carbon that 1 carving away from the oxygen would also be exactly the same they would absorb radiofrequency energy the same frequency and they would admit that the same frequency so in other words just like counting the number of peaks in the carbon animosity sector I couldn't immediately distinguish between those 2 molecules and I don't need to know anything about what frequencies the absorbing emitting and I just count the number of peaks and that's easy to do and I expect you to be able to do that OK here's another compound Money start number and you use letter ABC if you want you can continue to use my number's carbon 1 directly attached to chlorine is another common hazard H attached to it doesn't really matter that there a tax that's different it's 1 carbon away from chlorine and I'm about to methyl groups and the 2 methyl groups will be indistinguishable if I flip this around us right there would be a plane of symmetry through this molecule so carded 3 over here is not distinguishable from carbon 3 on the other side those are the same did the same by symmetry there symmetrical with each other so I would expect only 3 signals for this coral butane molecule here for this it's actually 2 metal 1 Coral propane but the bottom line is that those 2 carbons there a symmetrical and the same I could spin around the trading dropped this other spinning around and have a very thin tenure but if I spun around this bond I could get those 2 carbon atoms to experience the same environment became a 2nd look at a very similar-looking molecule here and carbon 1 year direct it's part of the Al-Qaeda strictly attached to the chlorine and other mother got another carbon that has no chlorine attached I could definitely distinguish those but what's tricky hero this attached to metal works and those are not the same there's a another group over here that's on the same side of the court as the chlorine atoms that assisted the chlorine and then there's another method group and it's different is trains to the court and you can spin around the double bond to submit its since molecules don't do that this methyl group on the other side is different from current 3 normally like carbon for a wonderful group assessed according the other methyl group is Transtar clawing and they don't interchange there's you have to spin around the double-blind double bonds don't do that so here I would expect for signals in my comment and it's very easy and I could look at the current market instantaneously all peace maybe that's a match maybe it's not but if I see 2 peaks my mark that's a pretty good indication it's not the right molecule with the spectrum doesn't match the OK so here's another and I'm trying to make it look complex and fancy here to throw you off so here to Koblenz that are attached to the oxygen animals the labeling them as 1 carbon number 1 here to ages attached there is no other carbon like that in this molecule His carbon number 2 that as a hydroxyl group attached that's distinctive and unique as no other comment as a hydroxyl group attached Nova currently has a medical groups ticking off of that there is no other carbon like that and the 4th carbon in structure is just another group that's distinctive then this would exhibit for peaks in the car with 13 spectrum so I expect you to be a little work through this and identified on how many people you would see in the sea 13 spectrum written aromatic compound in and I think it will help us if I draw the resonance structure of this so he started by taking these double bonds and a draw and we're going to do a lot more resonant structure drawing upcoming chapters when I dropped the resonance structure for this month at the point is you can't just look at the positions of the double bonds and decide this is an equivalent representation this resident structure appear this is an equivalent representation of of this tie Coro benzene molecule it's exactly the people and the important point is that at the start number in my province that was supposed to be an alcohol superior Court so-called ethanol was the name of this molecule OK stock number and my the carbon atoms I'm going to label the service next to the hydroxyl was carbon 1 and then when I walked 1 carbon Nova there's 2 different apartments the 1 card away from the hydroxyl and there are identical and you can use the positions of the double bonds to tell you whether the same different because when I draw the residents structure now the carbon to up above here is double bond and so you have to keep that residents in mind to understand the equivalency of to into now I'm not 1 for carbon further over I've got to have those as well those are identical by symmetry and then finally when I look at this the last carbon it's next to the chlorine and is only 1 of those sold by Panama because of the equivalence of carbon to win too and carbon 3 and 3 they won't give different peaks carbon to into walls will absorb and at the same frequency and carbon 383 will absorb an amended the same frequency and so I expect only 4 peaks in the carbon 13 spectrum for this molecule OK so that seems kind of abstract so let's take a look at our 1st anymore spectrum of it's a carbon emerged after months of trying to interpret this and this is typically the situation in I find something everybody all the books tend to make up stupid problems like this there's no basis in reality I'm walking in the lab and I find this mysterious bottle just sitting there that's labeled C 2 H 4 C O 2 and I don't know what it is here's the C 13 and Maastricht you tell me which 1 of these 2 molecules no nobody just walks into the ladder finds mysterious bottles like that but usually you make things you're not sure which made synthesizer bore you isolate them from nature OK so the 1st thing you should know this notice I see 2 peaks in 13th factor and you have to figure out maybe they both should maybe both of these chemical structures should exhibit to peace but at least we can ask how many people do expect to see so I'm going to start over here with this with this 1 one-day coalescing over here and I see this carbon regressed to according detached carbon ones and I said ,comma there's no cords attached that's definitely different there's no way that the Cottonwood recordings should absorb and emit at the same frequency is the cotton has no core I expect to signals is in the 13 spectrum for that and look there got to signals but what about this other guy ,comma I think 1 to die Clairol I I look over here the left-handed carbon unit has 1 client attached but then I look over here at the right-hand column it also has 1 chlorine attached I look over here the left-handed carbon and it's 1 common away from the 2nd quarter will also is this right-handed got there is nothing you can do to distinguish between these 2 carbon atoms that I want to die "quotation mark will get exactly what he can the carbon spectrum there 2 cartons are indistinguishable and the very fact that I see 2 peaks here in my comment and what spectrum has immediately resolve this issue by immediately know it cannot be that because that should give 1 peak where is that should give to peaks and I don't I don't need to know anything about the frequency of absorption for that very easy to resolve all that only 1 of those can possibly match look here's a set of 3
ice America compounds was just see how we can use this symmetry and 3 spectral astride a maximum of each 1 of those compounds matches with 1 of those 3 spectra but see if you can predict how many signals you expect to see but Indiana March spectrum OK so let's start appearing How many different signals would you expect to see for top compound with some elected it's not matched to the specter on the side yeah expect to see 3 excellent so I come over here I see there's a carbon it's attached to portable here's another 1 that's attached to court exactly the same just flip over the molecule horizontally and you will be able to tell the difference there's a car that's too that's separated by 1 comment from the chlorine atoms and on the other side is symmetrically disposed carbon-have seen then I come down over here in years now carbon it's far away from quarries and there's a carbon Donna that's equally far away you cannot tell the difference between these 2 carbon 3 by carbon and OK let's take a look at this next molecule Moscow many peaks to expect to see for the next March In the 13 spectrum how many different types of carbon atoms are there "quotation mark so I see Carboneau that attached to according and over here covenants attached to according identical and now walk upstairs here not see this carbon it's in between the 2 chlorine atoms is only 1 of those that's unique and I'll go farther away down here there's a carbon that's attached to carbon 1 so it's separated ,comma 1 have we another 1 I could say exactly the same thing about this and finally there is only 1 carbon atom here so I should put 3 for them just to give different numbers not the bottom of this molecule there's a single carbon atoms it's as far away as it can possibly get it's absolutely distinctive in terms of the as 1 age attached its 2 carbon separated from the chlorine so I expect to see for peace so this would have 3 peaks this would have for peaks peaks I'm doing the job writing not come down here is bottom molecule and you can see the surprising effective symmetry start numbering problems using carbon ceramics the chlorine down below there 1 6 according the same and I come over here it's 2 o'clock and I see a problem this 1 ,comma everywhere away from a chlorine but you could say the same thing for this other carbon on the other side and when I walk down below this carbon number was also encourage operate away from corn all 4 of these carbon on the side are indistinguishable I would expect to see only 2 peaks in the animosity factory this conduct just by looking at the number of peaks in the carbon animosity factory and by using my knowledge of symmetry acting very quickly get a huge amount of information from the province some 181 last million-dollar secret before we finish up here and then I'll explain on how to use the chemical shift to make sense of this year's a million-dollar secrets don't interpret carbon Mark and to froufrou so carbon don't have attached hydrogen give small peaks so I look at these benzene rings some problems that have no hydrogen is attached to me of chlorine atoms look at that there's carbon 1 that the great there has the chlorine no leeches attached look over here and that the spectrum ball you to match it up the tiny peak there has a chlorine attached no hydrogen and then this last compound over here that there's a carbon with no hydrogen injection according that's that's more detail and you can use that Al-Qaeda safe respect OK so it will pick up where we left off on Friday and then from talking about proton animal
Aktivität <Konzentration>
Humangenom-Projekt
Tiermodell
Stoffwechselweg
Memory-Effekt
Chemische Forschung
Gesundheitsstörung
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Lösung
Chemische Verbindungen
Computeranimation
f-Element
Elementenhäufigkeit
Molekül
Spektralanalyse
Organische Verbindungen
Fülle <Speise>
Zellkern
Setzen <Verfahrenstechnik>
Primärer Sektor
Gekochter Schinken
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Spektralanalyse
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Tritium
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Computeranimation
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Altern
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Disposition <Medizin>
Alignment <Biochemie>
Massenspektrometrie
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Acetonitril
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Tube
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Setzen <Verfahrenstechnik>
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Teststreifen
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Propionaldehyd
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Marker
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Altern
Chemische Struktur
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Kohlenstoffatom
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Chemische Verbindungen
Protonierung
Injektionslösung
Altern
Sekret
Chlor
Chemische Verschiebung
Sense
Vancomycin
Benzolring
Molekül
Darmstadtium
Chemischer Prozess
Kohlenstoffatom

Metadaten

Formale Metadaten

Titel Lecture 17. NMR Spectroscopy
Serientitel Chemistry 51B: Organic Chemistry
Teil 17
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 10.5446/19486
Herausgeber University of California Irvine (UCI)
Erscheinungsjahr 2013
Sprache Englisch

Inhaltliche Metadaten

Fachgebiet Chemie
Abstract 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: 00:09- Mapping the human brain 01:34- Can we see Chemistry Inside the Brain? CHAPTER 14- Nuclear Magnetic Resonance Spectroscopy 05:52- 14.1: Which elements have magnetic resonance properties? 12:47- 14.1A: The NMR Spectrometer- A Superconducting Magnet 16:38- 14.1A: Energetic Differences Between Two Nuclear Spin States 19:39- The Sound of an NMR Spectrometer 21:03- 14.1: Why we perform H NMR and C NMR separately 23:10- 14.1A: The NMR Spectrometer- A Superconducting Magnet (revisited) 24:16- 14.1B: Strange Terms Because Every NMR Magnet is Different 31:32- 14.1A: C NMR is simpler than H NMR so use it first 34:56- 14.2: How many signals should I expect in the C spectrum? 43:40- 14.2: How many signals should I expect in the C spectrum, Slide 2 46:05- 14.2: Use Symmetry to Predict the Number of C Signals

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