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Lecture 16. Infrared Spectroscopy + Ch. 14


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saw this news article on NBC summoned added there was a link to an NBC News website that was talking about a super on phobic material managers had so many buzzword in there that I thought there must be some cool organic chemistry thing associated with this super on the phone with I'm no Latin expert but I can guess that means hates everything but I can tell from these pictures here so I went and looked up the paper that when you go read the original paper in the Journal of the American Chemical Society as much nicer pictures and they had on the news article which you can see is here's 6 different liquids they put droplets on this material completely different types of liquids in terms of chemical properties and you could see this this fabric that's been coded totally repels every 1 of these completely different types of liquids usually things repel water don't repel whale or organic solvents and vise versa and here the actually just to show that all maybe you just said that little drop down there really lightly maybe that's why it's not soaking and so they took these streams the jets of these droplets in a new them and you can see they're just bouncing right off of this coded material so it's pretty incredible that they're able to coach material I'd like to have a raincoat made out of this or not but I expected ever rain excellent Mina Hector dating from the skies but but that's pretty cool that's something that's that repellent maybe means I won't stay my clothes anymore sticker look molecules that underlying this stuff was developed by unleashed
Uday has attain does Group at the University of Michigan and he's a materials scientist and what he did as he took this match any code that match but with this very special mixture a sort of spray coating with a very special mature and if you zoom in on this very tiny section where it's been spray coating you see that when the spray coating dried out in left behind this is very fine network of of of dried out materials and here's what he straight coded at the molecular level that could zoom down to the levels of Adams and bonds you could see the material that is frequented this with any says in the paper intellectuals spun coding of cross-linked PMS plus 50 with resent Florida's will pass state was so there's little it's stuff means only dimethyl sidewalk scene is a very common polymer so he ever hear the people use the word silicone polymer This is what silicone is it's a bunch of silicon oxygen bonds in a framework and there's alkyl groups hanging off of that and it's generally very greasy usually likes to attract organic solvents so I would expect organic solvents to To too wet material it's coated with with sigh locks in polymers but when he did makes this polymer with these little nanotubes and this is what costs means that the you'll the merits so fast clock saying solar still SES block saying how much or how long those have been around 2 decades the tiny little man accused of sidewalks in polymer so if you could imagine making the Cuban Missile lock seen polymer you can see those same silicon oxygen bonds in there but this particular 1 dangling off the corners of each of the cubes is a little piece of Teflon for those per fluorinated out that's what Teflon is about to say is that these little man accused of Teflon mixed in with With greasy sigh polymer dries out Mom physically and this is not purely a chemical issue it forms these these spaces that it's simply do not allow water droplets to push their way by the important point behind us as you can see that there's gaps in here so in other words this fabric material is permeable to air permeable to gasses per meal to water vapors and yet it still repels droplets of many different types of liquids and I think that's kind of a creative use of chemical properties physical structure but to achieve some desired effects of maybe someday you'll be raincoats that it brief better armed and yet still can repel nerve gas agents of from Rainer whenever stocks falling on you from the skies OK so that's a very cool use of organic molecules with some little bit of the organic silicon chemistry mixed in but Monday's university holiday and I want to remind you that on the 1st day of this class I urge you to drive like business and so you have to make a decision which is going to do with your Monday and you're exhausted right you've had examined after the exams I promise you if you spend Monday morning doing organic chemistry even military university holiday you will feel so good in the afternoon and so accomplished I think how good you will feel if you have the courage to sit down on Monday morning and and do some spectroscopy products so that we urge you to do that but as we are now starting and spectroscopy we spent a lot of time learning all kinds of new reactions were going to learn more willing to take a break now and start learning reactions in it's going to get rusty it's up to you to keep practicing hard to keep your your chemical reaction mechanism still strong so we're all let me turn up the Michoacan easily speak louder about returning my calling look at this they were going to start and spectroscopy I'm going to start off like of Chapter 13 is not mass spectrometry infrared spectrometry and mass spectrometry is the kind of bilateral trade quickly walked through this and explain to you why won't have amassed commentary questions so that would start off with if you printed sort of blank course notes online this 1st page basically filled in for you there's nothing much for you to write I just wanted to be able to talk about what is master commentary when you go in there but when you go into the airport they sometimes will grab people of the line and swap them down and then you something very much like a mass spectrometry mass withdrawal it's not exactly the same in order to to measure whether you've got bomb residue of explosives on you know and so on the planet friend now the rover Curiosity has little probe that's digging sniffing and it's easier mass spectrometry to sniff organic molecules so sort of mass spectrometry and what's good for the idea behind the mass spectrometers you take a vanishingly small amount of sample takes next to nothing to do with my announced there so small you can't even see them and then you you will apply those that at the entrance to a big instrument that he up that and tries to lactic into the gas phase so your simple molecules start to enter here and then they hit this incredibly high voltage and that high-voltage will written electrons off I have a zillion volts positive on this plate over here on this little metal plate it all written electron out of your organic molecules and insert the organic molecules missing in electron it's now got a positive charges it will start freaking out and falling apart it's got all this energy and if you're molecule has a positive charge on it you can now use a negatively charged plate right here that's this blue thing but it is only the label of negative you can see the negative charges here diamonds will get accelerated to that negatively charged .period and you can make it so that they accelerate and moved to this tiny little slipped and out all your fragments of your molecule is stopped that started to fall apart now moved through spectrometry and into a magnet and the key is that in a magnetic field ions are affected by the magnetic field of I've got a positive charge if I have a positive charge and I can see a negatively charged plate and start moving toward the negatively charged plate that I see a positively charged played it's over here it's going to repel me so this magnet distorts the trajectories of these ions as they're moving quickly in this little streams and finance the very heavy will it's very hard to change the trajectory they keep going almost straight in the bank into the magnet and don't go anywhere I answer to light it too strongly attracted To the negatively charged part of the magnet to the negative part of the field and ions that had just the right mass will continue to move in just the right trajectory so they can be received by the detector the guy so you can adjust the magnetic field and skiing and the strength of the magnetic field so that you can you can scan the C on my irons light are they medium-sized or they have that's a mass spectrum and it is so sensitive you can distinguish between alliance the differ by a massive 1 that's the idea behind mass spectrometry the 2 mastectomies really just a plot of all the little chunks of molecules and that carry a positive charge OK so you'll never run a mass spectrometry experiment in can 51 series on let's take a look at a mass spectrum so if you're reading this weekend partying down somebody gives you a green tablets and you bring it down to a mass spec facility of over here and wryness and sniffer analysis you get a mass spectrum looks like this submitted for EDI analysis so here's what it looks like when you suck electrons ecstasy and DNA and if you suck electron will come out of the most nucleophilic most energetic electrons that this lone pair so to leave behind a positive charge right here after you suck electron out of nitrogen and then with all that high energy this will start to fall apart so you're you're ecstasy and that's missing in electron now is a positive charge it starts bonds start popping up upon the Cleaves years Obama Klee's annual CDs fragments in mass spectrum and if you spend years studying these you'll be able to just look at the fragmenting guests with the original structure of the molecule so right here that the molecular what's called the molecular ion and all of a list that for you molecular ion we usually call this nonplussed plus by say and plus means that's the molecular ion and the only thing missing is an electron conceded as a massive 93 she already have a pretty good guess I wasn't cut with some from worthless anesthetic that's the real deal they gave all this stuff over here this debris those year fragments and they all have a positive charge otherwise they wouldn't have moved in In the magnetic field on you know the fragmentation process gives plenty of neutral fragments as well but you can those by mass spectrometry so this makes this fragmentation is both powerful because you can deduce chemical structure from that but it's also very complex it takes years of practicing to learn how to look at these fragmentation patterns and really make guesses as to what the original structure was so I will never ask you to interpret mass spectrum like this from ever ask you to look at the fragments and guess what was there and I think that those are important
skills but not at this stage and I don't think any of the other sections in camp 51 0 we are asking you to interpret fragmentation patterns so really the most useful thing is knowing and molecular formula that you can make some good guesses as to whether you've got the right stuff just by looking at the molecular form that the weight of that molecular where the man OK so How typically used it is this used to so that 1 very powerful thing you can do if used high-resolution mass spectrometry and in other words let's imagine that I have some peak in my mass spectrum here instead of just saying that has a massive 30 I really really measure accurately and determine the masses 30 . 1 0 0 0 1 0 5 4 down to the 5th decimal place if I can measure accurately enough I can distinguish between various clients that all have masses of 3rd and so well .period out you visited many different types of species that can have a massive 30 years 3 possibilities right here composed of carbon hydrogen oxygen and nitrogen so formaldehyde C H 2 0 as a massive 30 . 0 1 0 6 but if I have to nitrogen into hydrogen that also has a massive 30 it's just slightly different but it is different you know I take ethane gas that also has a massive 30 but it's not exactly the same as formaldehyde and other words these 3 different molecular formula all have a slightly different matter if you measure it accurately enough and so high resolution mass spectrometry gives you a number that is so accurate that you can distinguish between various molecular formula In other words if I give you the exact Massu could go to a table and look up the molecular formula no why does that work it works because of protons has a different mass from the neutron right they don't all have a massive exactly what they're different up to about the 4 decimal place and an oxygen atom has 8 protons and neutrons in it but if you look at the massive carbon plus for hydrogen is it's similar they're both about 16 but that's made up of 10 protons and 6 neutrons mood and there's some electrons in there so because the Proton has a different mass from neutron that's what allows you to if if you measure accurately enough to back out the molecular formula so hypothetically on my exam I can give you an exact match and then give you this big huge table and then you could look up the molecular formula in the table and what a waste of your time would be some going to do that instead I'm just going to give you the molecular formula and will just pretended that came from that spectrometry I will always give you a molecular for but if I do what you can assume we got that from mass spectrometry so I will ask you to look at mass spectra on my exams and will ask you to interpret the exact masses on just going to give you molecular formula and it's very easy to get those From there for mass spectrometry for gettin terrorist discussion of mass spectrometry it's powerful stuff on but the way we used to use it most commonly nowadays ,comma is this kind of at this level it's giving us information that that you don't need to interpret fragmentation patterns and look up the and molecular formula tables that's not the way spend time so now that switch on to our whole different before I go beyond that how are you going which talk about how you will typically be using the molecular formula so will be of a particular workflow a problem where I give you a molecular formula so here's a type of spectroscopy probably will see on my problem sets in discussion section on the exams that to book a problem looks something like this right you don't see mass spectrum there to worry over what you do see is that I've given you a molecular formula lady of giving you some chemical information I've told you the starting materials I told you the reagent I've told you the molecular forms of the product and all you have to do is figure out what the structure of the product is the problem with this is you know a lot of reactions of HCl the promises this some E-1 1 elimination innocent substitution reaction the best thing that you could do just to take the molecular formula and start to use it because it will give you some clues if I give you a molecular formula how you use that information is the way I would use it I look over at my starting material here and I see all to oxygen and I look at my molecular formula was only 1 oxygen but I have a pretty good idea but about what kinds of things might have happened it's from the 2 oxygen not still there the other thing that I don't see the chlorine atom so it's not going to be some 1 arrested 2 reaction because it a in the market for you could all do this this is very simple stuff but it's all based on a molecular formula comes from the spectrometry I expect you to be look at this and see all lost and oxygen coring see that's easy stuff that I expect you to know how to do the other thing that I expect you to know how to do this and I expect you to know that there's 1 degree of saturation you're now good at calculating degrees among saturation and if there's 1 degree of and saturation that tells me that I've either formed a bond a double bond or a ring so I know I have powerful information about what kinds of structures I should be drawing out so now it's up to you to just throw out some plausible structures that have 1 Bonderman wondering maybe I could pop this hydroxyl group offered acid and cycle as around that I'm much quicker than you are right now it figure out these possibilities so that would be if this hydroxyl substituted that 1 that only has 1 oxygen could be anyone elimination reactions maybe I eliminated the tertiary alcohol to give to give a double bonds on it maybe wasn't as anyone but I'm kind of already discounted that because obviously there's no chlorine in the molecular formula don't even need to think about that for a so anything subsidy would climb not even going to bother those out so really there's 2 structures here than in that match the molecular formula and I would need some extra piece of information to figure out it's kind of clear from looking at the molecular formula that I lost and hydroxy group probably the tertiary 1 and then something happened and so now on the bottom of this payout of this problem here I've given you and I are a spectrum In other words you want extra piece of information to help figure this out yes from the molecular formula you can back that up to you guys should how to calculate degrees on saturation from molecular yet we cover that it's like we cover and then we don't use it we forget about it so you will we lose a set of rules that I gave you from molecular form the basis degrees in Centereach OK see you you don't know how to look at Irish patriot and so I'll show you how to look at desire spectrum and in a fraction of an instant you will decide which of these 2 products here between these 2 products each here which of those of the products that you get in this reaction but this was talk about spectroscopy in general and then will hold man will spend the rest of the lecture talk about infrared spectroscopy This is an infrared spectrum on the bottom of this page and maybe I'll just tell you right now with the structures unit left guessing OK let's talk about spectroscopy usually as a general process here spectroscopy means absorbing on some type of electromagnetic radiation and looking what happens to the molecule so this 3 types of of spectroscopy that we will cover mass spectrometry is not spectroscopy mass spectrometry is not absorbing light it's mass spectrometry is pumping is ionizing molecules and literally destroying them or is having molecules absorb light doesn't destroy molecules of mass spectrometry is is completely different from spectroscopy on but spectroscopy means you absorb took some type of light and we'll talk about 3 types and each 1 has its own chapter so you be visible spectroscopy you shouldn't use that and can 1 Beer's law of absorption of visible light Inuit measures and extinction coefficient you could calculate the concentrations you by looking at the wavelength at which things absorbed you could make guesses about the structure of organic molecules and so too quickly which is looking at it with UV light causing electrons to move farther away from the nucleus so electrons and the tech terms that would be that they moved higher energy orbitals but the bottom line is that they move electrons move farther from the nucleus there were going to cover that in Chapter 16 will talk about you the visible spectroscopy and how chemical structure correlates with features that you see in the UV the visible spectrum in this chapter Chapter 13 we're going to talk about infrared spectroscopy and mainly what's happening when you absorb infrared photon is that bond start to vibrate and other kinds of actions that
induces ring kinds of actions but the main thing is that we're going to be concerned with with infrared spectroscopy is that we absorb infrared photon it's just the right wavelength your bonds will start to vibrate and you can look at those absorption is and figure out something about the structure of the molecule so that's Chapter 13 and then it in Chapter 14 Indiana we're going to be using radio waves of a frequency waves and here we were simply do his were flipping out nuclear spin is that supposed to be nuclear that were flipping nuclear spins upper down with radio waves so you and visible photons packed a lot of of energy if you can get an organic molecule to absorb no ultraviolet photon a visible photon you can get them to do some very crazy reactions infrared is not energetic enough to cause chemical reactions agrees with bonds vibrate and that he things the hot so if you go to a fast-food restaurant oftentimes they have french fries sitting under an eye lamp they're using infrared light to make the bonds vibrate so that on the food stays hot and then our nuclear magnetic resonance you maybe someday running and Maurise on an MRI magnetic resonance imaging has basically based on the same technique OK so was good and talk about infrared that's this chapter so next chapter will be anymore and then walked away to Chapter 16 to get to UV visible spectroscopy because let's go back and return Audi gave you a peak in I spectrum and I'm going to talk about 3 reasons why the IRA spectrum looks really done crazy and there's all kinds of reasons why they do it this way but in retrospect all those reasons are now 50 years old and I OK so 1st of all I hope is totally obviously the IRA specter upside down right on Monday referred to peaks in the Irish spectrum but a Peekskill go downward they don't go out and really added :colon balance so you have to understand when I use the term peak that I'm talking about an absorption and when when you're absorbing like those you see sort of Valley instead of a peace so I spectroscopy this through whatever reason decided to turn the spectrum down the reason they did that is there really plotting transmission of light in other words the light that can pass through a solution In transmission is the opposite of absorption so they were like you read this spectroscopy to plot how much light passes through but we're really going to be interesting absorption and you're not the transmission not how much light shines through your sample but how much light is absorbed by sample and so absorption goes downward and so when I talk about an absorption and I'm talking about things that go down again so that's 1 weird feature the other is higher seemed flipped around in other words normally when I out a UV Vis spectrum you start at low wavelength over here and a higher and higher wavelength over here on the right-hand side but look at the Texas here x-axis it gets smaller and smaller and smaller as you go to the right hand side the big numbers over here on the stock and as you walk across a gets smaller and smaller so that seems weird and it should at least should see where to use we go we higher respected in terms of decreasing bond vibration frequency and so I'm going to talk about on about frequency but what they've actually done here the reason why the axis looks like that is they'd actually planted in terms of wavelength so if you were to use units of wavelength than this access would be increasing that way and you're going to have to do some some kind of basis if you wanted it if you really wanted to go qualities make the point that the units here on TV near-normal units of frequency and I'm going to keep talking about Don vibrational frequency but these units here are units called inverse centimeters not about you but I'm used to hearing about frequency in terms of per 2nd 60 times per 2nd 100 thousand cycles per 2nd FM radio stations are measured in per 2nd and that's not a unit of time if you really want to convert this into hurts frequency you can use this on little equation that frequency equals the speed of light divided by wavelength and you can convert directly these on these inverse cm back into a frequency but nobody does that so I'll keep talking about frequency that you frequency in units of inverse wage numbers just seems really odd and better get used to that I'll say frequency but I'm going to give you inverse waving everybody that's the way the fire spectroscopy works so is entire spectrum of th season extending out smoking a joint this is the stuff that's it's getting you I will I see nearby Assistant ch stretches will talk about this I and OH stretch maybe there's some stuff here from the benzene ring OCC double bonds and a lot of useless junk social you might interpret the entire spectrum you see course of future me that I could not have told you that that was Delta 9
tetrahydrocannabinol but I could have pointed out the gross features of the molecules by looking at that IRA spectrum space let's talk about what is at the causes those absorption at the level of bonds and Adams What is it that's making a molecule by the absorber not absorbed and the IRA spectrum and this is it's it's the basic laws of physics so there's this hoax laws for springs that tells you that the vibration frequency depends on some kind of force constant for the spring stiff Springs Library very quickly floppy Springs Library very slowly and also depends on the masses your pulling if I to superheavy masses they don't move very quickly having things don't move quickly like things can move quickly when attached to a spring so if I think about how 2 balls are to Adams should respond when they're attached by about a springy bond it depends on the bond stiffness and it depends on the mass and pulling so I had this big huge mass this teeny tiny little Marcel by spring that spring can drag their tiny mass back-and-forth very easily by the tiny mass is easy to move you expect a very fast vibration frequency dragging a tiny little mass around hope that makes sense so small items like hydrogen should very very quickly the small Eddie Adams like carbon it takes time for them to move back and forth OK so just to carbon-carbon not carbon-carbon bond out the like your average everyday bond vibrating back-and-forth that I put a double bond between 2 carbon atoms not got to spring there it's harder it's it's it's this spring action will be stiffer so it's staffers you'd expect it to return back to its original position more quickly in other words at all more quickly vibrate back to its original position but you don't need to really think about Springs when you're looking at Irish spectra I'm going to tell you about some of the regions of the IRA spectra and I'll expect you to memorize these regions but they all can be explained based on books OK so 1st on that there's this region so I'm going to talk about wave numbers now here in this bottom access I'm going to refer to wave numbers so in this region here usually above about 3 thousand but it started about 20 500 is a demarcation line this is where I have all the bonds to H so another word bonds between CNH remember H is this tiny little light Adam Very High Frequency very easy to move the hydrogen atom nitrogen to H oxygen to age so bonds to age and of course we're never going to take the IRA spectrum hydrogen gas so you're never going to have to light Adams stuck to each other focus all the bonds to H appear past 20 500 wave numbers there is this kind of place in the IRA structure were you very rarely see things and this is where triple ones appear between 2025 ended wave numbers actually triple bonds are not that common even know we had an entire on Chapter 1 triple bonds I've got a C triple bond there the gun and triple bond here and I guess did carbon-monoxide in there you might but you know when I can analyze that now is if we have 1 fewer pipe bonds instead of triple bonds just double bonds it doesn't vibrate as it is we go from triple to double to single bonds we see lower and lower frequencies slower and slower vibrations so here CCW once NC double bonds and oxygen suitable ones carbon also the most prominent part of that region of the spectrum you'll also notice there's a difference between the massive carbon nitrogen oxygen I'm kind of staggering this a little bit of carbonyl oxygen is heavier than comments you should expect that the frequency for a carbonyl should be a little bit higher than for SEC double bond and there's another feature these differences will not out of here below 1500 wave numbers that's all the single bonds allergens attached to singalongs carbon-carbon bonds nitrogen carbon bonds oxygen carbon bonds this is referred to as the fingerprint region it's very complex and there's all kinds of other vibration modes here likes stuff like this which is not exactly a vibrational coupled modes were 2 springs actually vibrating coupled the concerted fashion and I'll give you 1 piece of advice that I'm going to follow I hope you do there's just to ignore this region but everything has C bonds you're not gonna learn anything by looking in that region just ignore it if I show you a spectrum and it's got all this mess in here just put your hand over right is that he's there you're done interpreting region so really you just look at his other half of the spectrum and you get information about all of them OH prominence or trip along double bonds that's what you should be getting out of IOC all this other stuff you might be tempted to use the southern region for I promise you will be easier by using animal OK so let's not take a look at go back and look at some spectra now we know these regions of the IRA spectrum it'll be very exciting to see if we can make a details of a section show 1
have 2 different OK so here's an IR spectrum of a molecule and that see if we can match the features of this molecule up to peaks again the pigs upside down to upside down peaks in the Irish spectrum so here is my molecule What do I see here in my molecules or that a sign on group there's a triple bond and look at that there's an absorption at 20 to 30 wave numbers that's a triple bond that's the sea in trouble 1 doing this stuff by bringing back and
forth I see some other stuff here from 3 thousand 72 27 wave numbers all those things right there that's the CHS vibrating and we'll talk about this but I can actually distinguish the ch is from the medical From the sieges on the benzene ring I expect those different vibration frequency and they do I can see them here in this I but I see this peak around 1610 which looks unusually intense to me and kind of surprised it's so intense but that's the pipe bombs related to this very morning now how can you get a chance to look at some molecules and see if you can identify features on our website there's a resources link in on on the resources have on the on the class website there's a link to something called the SDB has stated spectral database system the Japanese Web site but that has 50 thousand I our spectra for you to practice with the biggest type in molecular formula C 4 H 8 0 and you'll instantly come up with 50 I our spectra that you could look at and just look at the 1 Sunday OIC the cardinal stretch OIC the triple bond policy ch is nothing will train you to to interpret Spector around our spectra better than looking at AIA Spector an enema spectra if you take a class in surfing and you never bother to use the surfboard out of the late I promise you you will feel the surfing exam right you have to practice this stuff and the only way to practices by looking at many different spectra I can't stand here in lecture show you enough spectra so it's worth taking a look at and it's easy to do so again out here in a single bound region there's nothing just avert your eyes you don't need to see any of that stuff and I promise you that will be easier to interpret by looking at sea searching spectroscopy OK so not all bonds not all stretches are equally intense it's a lot so much talk about what is it that makes some peaks really intense In some peaks kind of small and hard to and the single most important feature that makes an IRA absorption contends is bond polarity in fact that's exactly what makes it possible to detect IRA signals His bond is Paula Is the polarity of a bond so that's a fundamental requirement to the bonds must be polar in order for you to see them in spectroscopy so let's look at these 3 types of triple bonds up on top here so I've got a scion of groupware carbon is attached to lecture negative nitrogen and here I have a terminal acetylene the eternal how kind where there's on 1 side of the al-Qaida's in our group and on the other side there's an H are not the same as doesn't have the same Elektra negativity Cardinal medicine Elektra negativity is age so that bond is a little bit Paula but if I take and how common it is exactly symmetrically substituted on you can't you can't excite is very simple bond vibration it's perfectly symmetrical because there is 0 dipole moment you have to have a dipole moment another word to different in Electra negativity between these 2 items in order for you to excited transition so it if ordered to arbitrate in slightly different you can sometimes see at a barely perceptible peak but I would never bother looking for that so what you expect is the most intense triple bonds will come from sigh you know groups where simple Al kinds should not be as intense this let's take a look at 2 very similar triple wanted molecules this is a molecule called bentonite trial it's a benzene ring with a scion of group moderate and down below I got almost the same molecule and the only difference is that the triple bond is a CEC triple bond and if we look at the intensities of the triple bond he here you can see that I've gotten labeled here so here 20 in this around thousand 20 500 that's where my triple bonds are so here is the scion of a triple bond the contends that wow goes on almost all the way to absorbing all the light and here's the CEC triple bond minutes almost in the noise there you kind of have to squint just to see that that triple bond there between the 2 carbon so here's the CEC triple bond right there here's that CNN triple bonded so polar so bond polarity affects the intensity of pink now there's 1 yes questions How do I know that this peak years the troubled bond because the only thing that appears on here from 2025 ended his travel documents and I memorize that and you need to memorize them so but that goes back to this this issue of regions of the buyers so the question is how How do I know that that that because the triple bond remember I told you that this region from 2008 500 wave numbers that switchable wants you and I've looked at a lot of Irish factory to make me confident that assignment and there's 1 other feature of that Of beside spectra that a lot of talk about shortly and that is look at this huge difference everything else looks kind of similar in the spectrum but what's this about it turns out that that's the Ch at the end of this year of the strip along very distinctive and all the other seated on the Benzema here but the ch that at the end of that troubled bond will talk about that in a moment will come contents that is a single bond is is way more intense and all these other sutures but together yes you know what was this is the work of the so why why deceived bonds have such high frequencies because it's very easy
to move in each of the surviving very quickly for his abiding cannonball attached plant it would move very slowly something like the spring can move very quickly something it's heavy it hard to move so along troubled understeer but still means that returns back to its original position very quickly because the spring is so stiff prison at some spring playing with its very slowly returned to original position but you know what I mean you don't even in Genoa looks like just remember those regions of the IRA spectrum is what you really ought to be doing and practicing by the inspector talking so the bond polarity matters a lot in terms of intensity OK so let's talk about the bond polarity and hydrogen bonding the kind of related so here's 3 types of bonds to 2 hydrogen atoms OH bonds in each bonds and see ones and of these old age bonds are more polar they are also better hydrogen bonding all age ponder better hydrogen-bonding than any bonds and only 2 Pontevedra hydrogen what a better idea demanding the siege by which he typically seen as item hydrogen-bond so because the the bond is more polar tho each time is more intense than in any H-bomb and I know it on his way way way more intense than a H bonds usually a single finding a molecule what is more intense than all the other H is added together so typically if and when I see a big lump like this the the technical term for this is this is a big as when I see that in my spectrum there's no question in my mind that there is either a hydroxyl group were carboxyl gasoline my molecule now if it's sort medium so I guess it could be a bunch of any but you even in an age which usually is a big lump isn't as big as this look how big the area's minutes stretching all the way down to 100 % absorbency so this is a molecule this entire spectrum of ethanol ethanol has 5 stages years those 5 CH stretches and that 1 LH is bigger than all of those other ch is combined so you always find has this is it's so powerful it absorbing and the effect of hydrogen bonding because there's so many different ways that I can orient myself to hydrogen bond with this it broadens the speak out you're actually seeing lots of little difference some versions of their which converts hydrogen bonded in different ways that's why the peak is so broad so hydroxyl groups carboxyl gasses there is an unmistakable dominant peak between 3 thousand and 4 thousand wave numbers and so I hope that when you see that kind of people it pictures you readily able to recognize that look at that I must have on can OH MY molecules and let's see if I can find that spectrum of detector hydrocarbon all because all direct you to have your attention to death when I looked at that it was hard for me to misstate the fact that 0 my gosh there must be an OH in this molecule you see that big lump there between 3 thousand and 4 thousand wave numbers right year capable of interpreting that an entire spectrum so I expect you to be able to recognize the now calls an agent can also also give big lumps to on and you have to look at inspector for a median ages versus wages in order to give yourself a sense for how much bigger than wages are in the IRA spectrum peso there's 1 extra thing we can get past the thousands of fur for Bonds connected to age whenever I get an IRA spectra it's not as tho all stages of the same ch is a different this year is attached to the end of a triple bond like this are stiffer the ch is attached sp 2 gardens says Governor ideas sp hybridized these comments on the benzene ring S P 2 hybridized and he's got going on in helping partner S P 3 hybridized and them below the more character 50 prisoners character on the stiffer that bond so as a result of this bond here so that the generalization is that protons attached to the end of an alkaline like this when I hear arch at the highest frequency and then if you're attached to a key you got the next highest frequency and then if you just attached to 1 Kane you're at not quite as higher frequencies that the stretches over here so there's this correlation between 8 attached alkaline 8 attached out teenage attached Ltd as to how higher-frequency and this 1 attached to the al-Qaida so distinctively it's way over here 33 300 wave numbers that protons attached Al-Qaeda usually kind of close to 3 thousand they're usually kind of close to the sp 3 hybridized so that's these right here and all these other ch is attached to the tail painted over here can you see there's a lot of those OK there's 1 thing I want you to do whenever you CCH stretches and that's to draw a line at 3 thousand wave numbers so let me draw that line I usually physically draw the line you usually just and you may not watch this all just take a piece
of paper and I'll draw a line in here 3 thousand Cancio using service that line is very powerful because when I look at on the right-hand side of this line that's for all my S P 3 hybridized ch is here after methyl butyl cycle Hextall all the singly bonded carbon that ages on those stretches appear on the right-hand side at lower frequencies and 3 thousand all the images are attached to double benzene rings those appeared slightly above or above 3 thousand wave numbers you can instantly gets information about whether you have pages attached out he's simply by looking to see if you have ch stretches above 3 thousand wave numbers and of course H attention kind is usually this the spearhead spike sticking out on
its own 3 300 wave numbers that's impossible to miss because it's usually so intense OK so draw that line at 3 thousand it'll help you to see whether you that it is attached outings when remind you not all out genes have pages on them so on the basis of a new now know everything that I know about interpreting spectroscopy maybe I have 1 or 2 more gimmicks but I just don't need to know that it's so let's take a look at a couple of spectrum will distract us here modesty how good you are at Edison that at interpreting ire spectrum would get to molecules were among the top yeah but this top molecule as 1 2 3 4 5 6 cartons attack saying and this other
molecule I think is hacks and all look at the other 2 spectra there which 1 is hexane at which 1 is sex and all the bottom line is Texas command that doesn't take any difficulty see largest in case you missed it here how could that that's so easy despite don't even need to look at the top spectrum undone but we could look at the let's look at the top spectrum because I can't resist by dividing the line 3 thousand wave numbers see how satisfying it is that although ch is the lower than 3 thousand wave numbers just in case I thought there might be a CC double bonds and financial there's not in over a year I see I draw the line at 3 thousand are harmonized all the CH stretches of below 3 thousand wave numbers of cases see how easy it is to use spectroscopy none that so easy and I just ignored all this stuff below 1500 it's just totally worthless for us OK let's practice again OK this is not a good 1 because I'm once again it's so easy I made too easy for you these tumult 11 months a molecular formula you could use mass spectrometry to distinguish these because they have exactly the same like the former you'd have to use something like I our spectroscopy so I gave it a mass that might be G. I don't know ,comma but when I show you it's absolutely clear which of these is the alcohol but what's even clearer committees which 1 is the key town I don't even have to look at the bottom spectra if I if I never showed you the bottom spectrum so I hope you can also see here there's this huge peak this is broadened peak at 34 80 that's the OH alcohol that's the OH peak so this bottom spectrum is the alcohol but I didn't need to look at the bottom Specter because there's an equally distinctive peak for and that is that this Group because its color carbon heels absorbing very strongly that's going to be 1 of the principal USA's for IRA spectroscopy for you and so the document I respect that I opted for the carbon you because its polar it's very strong CC double-bond don't absorb that strongly denied the Cardinals absorbs super-strong there usually is distinctive wage stretches in the spectrum let's take another look at this alcohol see that little tiny blip period 3 thousand 83 that's above 3 thousand wave numbers that confirms for me that there's a is attached to outings in this alcohol molecules and when I come over here to this other key Keaton molecule where I can see the commonweal I don't see anything past 2000 wave number it's all ch is attached to single bonded carbon itself there's all you know oftentimes if you can figure it out just by seeing 1 diagnostic PTI the art but there's usually lots of extra peaks can help you have information to prove that can get 1 last set of spectra here for you to interpret OK I have and a mild mannered and I have this Sano alcohol thing now it crazy about that is lumpy PQ but I also got this lumpiness over here is lumpy mass lumpy mass and I look at my molecules all there's this carboxyl met with 2 ages on here that's probably leading to a lumpy mass as eyedrops Alaska lumpiness now which is which which 1 is the Suyanto compound I don't as a sign of structure 22 16 that's the trouble bonded region from 2000 to 2005 ended with numbers so here's my scientist rhetoric there and when I come over here I see the stretches around 1700 that's the carbon that's the CEO stretches I don't worry about the 2nd pick at 16 1610 so you can see here this gives you a chance to see what the NH stretch of the NEH stretches look like awareness this blobby NHS years the OH business from my alcohol so that Sino alcohol is on top of is assigned a group there's the OH group and then this carboxyl it over here but has this not quite as blobby NH stretch and the big-time carbon OK so there's problems in the back of chapter that it wouldn't fire your knowledge expertise the practice of practice looking at lots of factories "quotation mark STDs databases looking like this factor practice
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Formal Metadata

Title Lecture 16. Infrared Spectroscopy + Ch. 14
Title of Series Chemistry 51B: Organic Chemistry
Part Number 16
Number of Parts 26
Author Vranken, David Van
License CC Attribution 3.0 Unported:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor.
DOI 10.5446/19485
Publisher University of California Irvine (UCI)
Release Date 2013
Language English

Content Metadata

Subject Area Chemistry
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. Topics Covered: Infrared Spectroscopy and Chapter 14. Index of Topics: 00:09- Superomniphobic material 01:47- Underlying Molecules CHAPTER 13- Mass Spectrometry and Infrared Spectroscopy 04:42- 13.1: The Mass Spectrometer-how does it work? 09:26- 13.1-13.3: Mass spectra are complex due to fragmentation 11:55- 13.4: The Exact Mass gives the Molecular Formula 15:14- 10.2: Use the Molecular Formula to determine Degree of Unsaturation 19:25- 13.5: Electromagnetic Radiation and Infrared 22:45- 13.6: Dumb Characteristics of an IR spectrum 26:56- 13.6: Key Frequency Regions of the IR spectrum 32:22- 13.6: Practice: Regions of the IR spectrum 34:58- 13.6,7: Polar Bonds Lead to Intense Peaks 39:35- 13.7: Hydrogen bonding leads to lumpy peaks 42:06- 13.6: Dumb Characteristics of an IR spectrum (revisited) 42:44- 13.6,7: Check if C-H stretches are above or below 300 cm^(-1) 46:00- Reading Spectra Examples

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