Transcript for:
Modern Analytical Techniques in Chemistry

[Music] [Music] hello my name's Chris Harris and I'm from a Lurie chemistry and welcome to this video on at excel topic 19 modern analytical techniques - so in this video we're going to be looking at all the information you need to know for Edexcel chemistry so if you are studying a level edible chemistry and it said excelled and this video is specifically designed for you so sometimes you can look at some information or some stuff online and you can wonder decide if I can wonder if it's actually in your specification and and if you actually need to need it you need to use it for the exam but with this video everything in here is dedicated towards that excel so you know that anything in here is relevant for you and there's actually a full range of videos for Edexcel ranging from topic one all the way up to this one which the last one which is topic 19 on my Alawis chemistry youtube channel they're all for free there's Lourdes there there's also some white board tutorials and there's also some exam technique questions as well so got looking at some past papers all I ask is that you hit the subscribe button that'd be fantastic to just show you support and as long as people keep watching them keep subscribing then I will continue to make them and also if you want your own copy of these you can purchase them from the link in the description box and the great value for money and they can be used on your smartphone or your tablet and it could be used on the move and you can even print them off and use them as part of your revision notes so so you're more than welcome to do that just click on the link in the description box and you can get ahold of them there okay so like I say this this information here is dedicated to the lxl specification and you can see it split into three main topics so you've got mass spectrometry which we'll look at first then we look at nuclear magnetic resonance which is NMR and then and chromatography as well and we look at combining the techniques or combine techniques of some of the spectral techniques that you need to know some of the spectral analysis that you need to know so we'll look at combining them as well okay so first I'm going to do is look at mass spectrometry so mass spectrometry is used to find the molecular mass of a compound so that's the relative molecular mass which is the M R and it actually has a spectrum as you can see on the left there of various lines and the lines correspond to fragments of the of the original molecule that we've that we actually put in under test and so we give it something called a mass to charge or MZ ratio and so MZ is just the mass of a fragment divided by the charge so as most have a 1 plus charge then this is just obviously same as the fragment mass so for example if we have a MZ of 45 that means that the mass must be 45 and this fragment if this fragment has a 1 plus charge then what this means is that and the 45 divided by 1 we'll just give 45s is the same as the mass of the of the of the fragment the peak at the end here called the M plus peak so the M plus peak shows the actual as is the mass of the original molecule that we had before it was put in the mass spectrometer and it was broken up into the fragments so this is also known as the molecular ion peak and basically this tells us the relative molecular mass of the molecule so in this case we can see here that this molecule has a relative black in the mass of 50 because the M plus peak is here so it's the most it's the most significant peak to the Wrights it's farthest right in the in the actual spectrum so this is a an M plus peak here okay so we can also look at something called high resolution mass spectrometry so high resolution mass spectrometry is really useful when we're identifying different molecules with the same molecular mass and rounded to the nearest whole number so you might for example have two molecules with a mass of 47 and so you know having a molecular mass of 47 it doesn't necessarily identify what compound you've got mainly because there's a lot of different compounds of the Mareth universe of seven and so therefore what we can do is use high resolution mass spectrometry which is used to effectively help to distinguish between molecules of the same mass so high resolution mass spectrometers they measure the relative mass to several decimal places so in like the standard low resolution ones which can only measure them to the nearest whole number so they're much more and and they're much more precise in terms of the the numbers that they give so let's have a look at an example here so we got ethanol which is ch3cho and propane which is c3h8 they have the same molecular mass NMR 44 to the nearest whole number now in a low-resolution mass spectrometer this means that you wouldn't be able to distinguish between these two molecules in particular because they would just give the same the same molecular ion peak that m+ peak would be a 44 so the way around this is actually using atomic mass data to measure the individual atoms to distinguish between the two so for example we use the data to measure the exact mass of carbon-12 now this one is going to be to four decimal places so you can see here that the mass of carbon 12 is exactly 12 so that's twelve point zero zero zero hydrogen is one point zero zero seven eight oxygen is fifteen point nine nine nine zero so these are the exact masses of each of the elements that make up some of these compounds in here so you can see the let's look at the molecular mass of our ethanol here which is our aldehyde so we've got two lots of 12 okay which is our two lots of carbon we've got four lots of one point zero zero seven eight which is your hydrogen and then we've got our oxygen here as well so if we add that up this gives us a mass of forty four point zero three zero two now if we do the same for and CH 3 CH so this is your propane and we do exactly so I've got three carbons and eight hydrogen's that gets us forty four point zero six to four so we can see here there is actually a difference and because there's a difference in the mass we can actually identify which one could be ethanol and which one could be which one is propane by just looking at the the figures to four decimal places so see with a standard resolution or the low resolution mass spectrometry these would both turn up as 44 but obviously using the high-resolution one we can actually distinguish between them okay so we're going to look at something called NMR spectroscopy so NMR is is quite a difficult concept and what we're going to try and do is explain how an NMR machine works and then what we're going to do those are then going to look at how we can interpret the spectra the different types of NMR machine how we can interpret the spectra and then obviously I'm trying to identify some molecules so we're going to start it is quite tough it's probably one it's probably one of the most difficult aspects of chemistry's trying to understand NMR and interpret their spectra but I hope that we can try and simplify it a little bit more by talking through the information that's on these slides here and so just before a star actually NMR machines are used in used in hospitals quite a lot and but they call them MRI instead so they don't use the word NMR so can you think why they call why the change the neighbor even though the instrumentation is the same don't you know the actual the actual analysis of it is the same so do you know why they've actually they've changed it to MRI instead of NMR so well there I'll tell you that towards the end of the video I'll tell you the reason why so see if we can see if you can ever think it's a bit of a bit a bit of a stranger beyond the obvious obviously but it's a bit of a strange one so nuclear magnetic resonance NMR is used to help determine the structure of a molecule so unlike some other spectral techniques where they don't really focus on the structure they look at functional groups or they going to look at and mass fragments or they're going to look at they're going to look at say we're going to do elemental analysis where they're looking at the different types of elements that's in there this one is much more NMR's much more useful for actually determining the structure so it can actually determine or distinguish between isotopes for example so there are two main types of NMR so this carbon 13 which tells the information how carbon atoms are arranged and this high-resolution proton NMR which tells the information about how hydrogen atoms are arranged to this two types so we're going to start with saying that if an atomic nucleus has an odd number of nucleons which is protons and neutrons then it has a nuclear spin okay so the nucleus is obviously in the middle and these nucleon spin in a particular direction so you can see with the diagram they're trying to illustrate that and so this nuclear spin actually creates a weak magnetic field around it and the NMR machine is detect how these magnetic fields are affected by a larger external magnetic field so what we've got is our nucleons spinning in a particular direction and they've got a mini magnetic field and around them they've found them here okay and obviously that can be influenced by another magnetic field an external one okay so as long as you know that so this is looking at an odd number of nucleons okay that's going to be quite critical because we'll look at that later in terms of the type of spectroscopy that we look at that we're going to look at okay and so hydrogen has one proton and so it does have a nuclear spin because one is odd it's an odd number so carbon normally has six six protons and six neutrons however some of the carbons about one percent of the carbon is actually carbon 13 which is clearly an odd number because it contains seven neutrons and does have a nuclear spin okay so when we're looking at different types of NMR you can see that we've got two types two main types there are other types of are but two main types is carbon 13 which is an odd number because we're looking at and we're only going to be looking at carbon 13 spectroscopy because carbon 12 got an even number so that doesn't work even numbers don't work in NMR and we've got a high resolution NMR which is a proton in the mass of protons are obviously odd-numbered as well so they've only got one in there okay so these nuclei what they do is they spin in random directions however when an external magnetic field is applied they align in two directions okay so this is remember all this bit here is just going into how an NMR machine works and the reason why this is important looking at how an NMR machine works because if you understand how it works and makes it a little bit easier to understand or appreciate what these machines can do and also how they can actually how we can interpret the spectra and what the spectra actually means so nuclei they spin either in the direction of a external magnetic field or they spin against it and those that spin in the direction of the field and have a lower energy so if we have a look here just first at nucleons a nucleon spin in all sorts of directions and different orientations and so the arils you can see on that diagram represent arrows the nucleon spinnin in in random directions and there's no external magnetic field applied here so they're pretty much doing what they want okay and energy is you'll see this diagram drawn in a bit where we have the nucleons that are aligning with or against the external magnetic field but you'll see that actually there is an energy line here so the higher up we go in terms of this space here then the more energy these nucleon have so for example this nucleon has a higher energy than this nucleon down here because it's higher up this is going to become more relevant in this section here okay so let's have a look so what we're going to do is apply an external magnetic field to these nucleon and see what happens so remember you've got some that will align with it and some that will align against it and so these ones are so the these ones are aligning with it have a lower energy level than those that aligned against it okay that's obvious remember if you've seen my other videos and then you'll know that I always say that atoms and molecules and nuclei or for example and neutrons and protons there they are incredibly lazy and they always want to be in the lowest energy form possible so to have these orbitals here sorry to have these nucleon spinning at a higher energy level and that's not a stable form but they will obviously they will align against if it's if they were lining across in that in that direction anyway and obviously there's a magnetic field that's forced them into a fixed direction and so what NMR does it fires out radio waves and a specific frequency at a specific frequency the nuclei are aligned with the magnetic field absorb the energy and they flip up into the higher energy level against the magnetic field so we put energy in to put these nucleon in a higher energy state okay so we use radio waves to the NMR machine first of all applies an external magnetic field and then it uses radio waves to effectively move some of the nucleon from a lower energy to a higher energy okay so those with a higher energy so those at the top there these can drop to lower energy and they can emit radio waves as well so they move up and they move back down again because they want to be in that lower energy state but as they do that they emit this radio wave and then initially there's more nuclei aligned with the magnetic field so there's a lot more there because that's the lower energy remember and so overall energy more energy as absorbs then is emitted okay because we've got more actually being migrated up into the higher energy level and so therefore NMR is measuring the amount of energy that's been absorbed such an how much energy was required to move these nucleons up into the top level now that gap the difference between that so remember this is nucleons within one atom okay so the difference between here and here is very much dependent on where this nucleon is near to so it's influenced by other other nucleons down so for example if this is a carbon atom these are the nucleons within a carbon atom if that carbon atom was bonded next to another atom say like an oxygen that oxygen would have an influence on how easily the nucleon in the carbon atom moves from the lower energy to the higher energy so this gap can change and obviously this is then where we start to use NMR strength in actually we can determine you know depending on what the gap is here we can determine what's next to that carbon atom so this is where we can say and the marking detect or tell us a little bit more about the structure of the molecule that we're looking at okay so just carried on with that so the energy absorbed by the nuclear I like to say is dependent on the environment that it's in okay so all everything to do with NMR is mainly to do with what's around the atom that we're looking at and rather than the actual atom that where where look that we're actually investigating so so it's very much dependent on that environment so the reason why is we can get a nucleus can be shielded from external magnetic field from electrons surrounding that nucleus so for example remember we've got an atom with a nucleus in the middle and around that nucleus we have electron shells now them shells effectively act as a protective mechanism so they protect the nucleus inside from the external magnetic field so for example if we've got a lot of shielding around there then it's going to protect it a lot more if it hasn't got as much shielding around there then it's going to protect it I'll see a lot less so it's a little bit like suppose if you put a if you roll down a rocky hill for example I wouldn't obviously wouldn't recommend this but if you roll down a rocky hill with no protection on at all so you've just got clothes on then that's gonna hurt quite a lot because you're gonna feel every bump and everything and if you then decide to come we'll do exactly the same I'm gonna wrap yourself up into in bubble wrap let's say so you put some protection protective coatings around you then actually you can roll down that hill and you're probably not going to feel the bumps as much so because you're shielded from the effects of that external you know the rocks effectively so NMR is exactly the same except our protection or protective mechanism is the electrons around that which is shop which is sheltering the the nucleus in the middle but this protective layer can be influenced by being next to something else another atom which can perhaps take some of that protective layer such as an electronegative element that can pull them electrons away from the atom that's shielding the nucleus and that can have quite an influence on you know how much how much the external magnetic field affects it so let's carry on so atoms and groups of atoms adjacent to that nucleus they could say they affect the level of shielding so for example mentioned this before but electronegative elements such as oxygen near a carbon will reduce the electron shielding on the carbon atoms so an oxygen will pull some of them electrons that while shielding the nucleus in the carbon atom and pull it towards the oxygen so that means that that carbon now is more susceptible to influence from the external magnetic field okay so I hope you follow and so far okay so the magnetic field will be felt like to say by the nuclei differently depending on the environment is it is in as they absorb different amounts of energy and various frequencies okay and so it's the difference that the NMR spectroscopy is picking up so remember it's the the NMR machine is measuring the absorbance how much energy it requires to turn one of the elect one of the nucleons with the magnetic field into the higher magnetic into the higher energy level excuse me so so obviously depending on the shielding what in what effects that is the shielding and the shielding is impacted by what that carbon atom or hydrogen atom because this is the type of animal we're looking at and what that's actually next-door to because that will obviously affect the level of shielding okay so I hope that's making sense so far so that pretty much explains it but just to finish off on the actual mechanics in terms of how the machine works the environment is determined by the groups of atoms that exist near to the nuclei being examined and we look along the full chain not just the atoms immediately bonded to the atom being examined so it's a little bit like if you've got a street okay and you've got for example if we've got a neighbor that's perhaps cutting the grass at the front at the front of the house okay so you might have other houses down the street which are influenced by that person then I think or they're cutting their grass so I'll cut mine as well at all cut the hedge or you know whatever whatever you're going to do so um so you can see that actually the street is a bit like each house is a bit like a carbon atom okay all the way down all the way down the street and so therefore you know somebody cut the grass it number number one where me infrared somebody at number three which is next door and that may then influence some Viet number five or even number twenty seven down the further down the road might actually then have an influence on what number one's doing so you can see that there is an influence in in terms of a street it's a bit like a long carbon chain so carbon chains are exactly the same you've got one carbon atom but it is influenced by the full range of molecules down you know down the carbon chain and down the other way as well so so there's a lot of influence here and we'll see how this fits in later on but for an atom to be in the same environment it must be bonded to an atom or group of atoms that are identical and we'll look at some of the next some of the next slides will help us to identify this so basically if we've got and say if you've got a house so you've got one house and there's only it's only a house of three three houses and only streets over three houses and see that the house in the middle and that's going to be next door to another house and there next door to another house okay so left and right of each other so that house is in the same environment because it's next door to two identical houses left and right of it okay and there's no other houses around so so you can see there there's actually a level of symmetry so you can see the next the two houses either side are they're in identical environments however if you look at the end house when the end house is that's not an identical environment because to the right of the house this green space and to the left there's another house and then to left again there's another house so it's the one in the middle that's in the same environment but the ones on the end obviously in the same environment for them because they've got green fields to one side and then they've got you know house the house in the middle to the other side so if you can try and imagine that and this is exactly the same principle with carbon with carbon and proton NMR is where all we're doing is we're looking at what's next door what's influencing that carbon or hydrogen in the middle okay so we'll have a look because I think the best thing with these is to actually have a look at some examples so you see what I'm talking about but this is gonna be quite critical because carbon environments or identifying environments is going to be really pivotal in terms of you understanding NMR okay so let's have a look so look a look at some samples that looking at how we can identify carbon and hydrogen environments okay so so look at this one so this time we're just looking at we're looking at carbon 13 NMR okay so we're not looking at protons will look at protons later but we're looking at carbon 13 NMR so you can see here we've got a molecule okay down to color coded the carbons to show you where these environments are so we can see this is a bit like a house a little bit so you can see we've got this carbon here is in one environment so it is bonded next to a ch3 and a ch3 either side and it's got a br and it's got a hydrogen so we look immediately left and right okay so that's one environment these ones here are in the same environment and the reason why this is this one means a bit like house you've got the end house here which is next door to a green field let's say there's nothing here and it's next door to this house in the middle which is CBR and this house is also next door to say green fields and it's next door to the house in the middle so these houses on the end are actually experiencing the same the same type of same type of environment okay so they're both facing onto this middle house and they're both facing onto that green fields either side so you can see it's the same with with carbon with these molecules here we can see we've got a one environment here and two here so these are both in the same environment so this molecule has two carbon environments or and put it through an NMR machine it will detect it as two environments we get two peaks okay so let's have a look at this one so all I've done here this is what I mean with NMR detect structure so all I've done is have moved the bromine from middle to the end and that's dramatically changed what NMR's reading so now we've got a house here with so this is a this is a house at the end here this is no next door to a garage okay so there's a garage on the end of this house this middle house here is next door to the house of the garage and the house without a garage and this house here is next door to green fields and a house so you can see all of them seen Orioles each one of them houses are experienced in a different surrounding so in terms of carbon NMR you can see here that we've got a carbon bring it back to from the house I'm gonna stop using the house analogy because I think you might get it but basically we've got this carbon here that's next to a bromine and two hydrogens so that's it there next to this carbon here which is obviously bonded to two hydrogens but it's bonded to a ch2 BR and a ch3 and this one is bonded to obviously a ch2 and a ch2 BR so all of these are all in different environments so they're not not a single one of them in the same environment so we look all the way across the chain remember okay let's have a look at this one so this time we're going to look at hydrogen environments because we need to know about hydrogen environments as well so this time of colour-coded the hydrogens so you can see here we've got these hydrogen's so there's two hydrogens here so these are bonded to a carbon with a br ok and the bonded to a ch3 and these purple ones here a different environment because they're bonded to a ch2 and a Br okay so they're both in separate environments you see there's no symmetry really symmetry is quite an important one cuz if we got symmetry that means you've got the likelihood you've got you know some of these carbons sitting in the same environment okay so that's a look at the last example so here what I've done is add an extra bromine to it and it's a we now have some symmetry here so these carbons these hydrogen sorry here are expect so our experience in the same so it's been in the same environment so they're both bonded to carbons connected to bro means so they're all in the same environment so at the NMR machine would pick up that there's only one hydrogen environment here they're all experienced in the same you know the same environment so and there's four hydrogen's obviously in this environment here and also Intel is symmetrical so where you've got symmetry and you have and you have less less and less tip you don't have as many different environments if you've got some symmetry in your molecule okay right so tetramethylsilane okay so TMS is a chemical that's used as a standard when we're looking at chemical shift in NMR spectra okay so this is quite important because you're gonna you're going to need to know how to spot this and why and you know why it shows the peaks that it does so nuclei what they do is they absorb diff about different amounts of energies at different frequencies it's really difficult to measure the magnitude of this without reference to a standard chemical to measure it against a case you've got to have a reference you've got to have a benchmark otherwise we don't have a benchmark you don't know how much energy is being absorbed you don't know if that's large you don't know if that's small and we use something called tetramethylsilane or TMS so for example then we do this all the time in science we've got to measure it against something that we have confidence in and that we can that we can measure it against to make sure that we can you know that if that value is zero then we can measure and we can measure that again so for example if I was to say isn't elephant heavy you would probably say yes okay it's very heavy if I was to say okay if I isn't elephant heavy in comparison to the weight of the earth you would say no it's incredibly light but the reason why you're probably saying that it's heavy is because in life we would benchmark constantly against something which we're comfortable with or something which we know so for example if we're looking at life weight we may maybe look at a we look at a car for example or we look at and shopping or we look at picking up objects everyday like a computer like a pen and all these things are quite light relative to us so when we look at other objects what we use everyday we compare them to them and we say that is heavy now that's fine but one person's heavy is another person's light so it's really difficult to actually you know vet you know justify you know these comparisons so in science we have a standard and we have a reference that everybody uses and everybody sticks to that same standard that same reference then that means that if a science in Germany scientists in Germany does this and science in Britain does this or a scientist in America or Japan or anywhere around the world they know that actually they're all being measured against the same standard and we can have confidence in comparing results okay so we use TMS so that's just with anything in science not obviously it's not specifically to this but obviously you know this is a standard but you know anything where we're measuring something we have to measure it against something we have to keep some things the same and change one thing so it's so so important otherwise you get results which don't mean anything so tetramethylsilane has this structure anyway so whereas I am a silicon molecule silicon atom sorry in the middle here and we've got methyl groups around here so hence the word tetra meaning for methyl cuz got methyl group since I'll a and I'll she was a silicon in the middle so TMS is 12 hydrogen's all in the identical environments and this will produce a really large single peak well away from other sample piece okay so and the good thing about TMS is that it's inert it's non-toxic and it's volatile so we can remove it from our sample so we mix our sample with TMS but we basically set we calibrate our NMR machine to make sure that there's TMS peak is zero and then everything else is measured relative to that so that's a standard when I recognized chemical to use in NMR and so the difference between the TMS peak and the Peaks produced by the substance under the test it's called a chemical shift and what you'll be given in in the exam is a data book or a datasheet and that will have your chemical shift tables on that so you don't need to remember them but you will see some examples in this video so we measure chemical shift in parts per million or ppm as because it's used as a standard to measure against and we assign this as Sigma zero okay so we say that it has a zero value and it means that everything else is measured measured relative to that so when we look at an NMR spectra you'll often see and this peak at at you're at zero as TMS is used to calibrate your NMR machines by analyzing a sample now you might find it might not be the biggest peak probably won't be you can actually alter it NMR spectra to emphasize Peaks that you want to know but the peak at zero and if they ask you any peak at zero has got to be because the TMS it can't be because of anything else okay so the peak at zero no matter how high it is it must because of TMS okay now you can see here just coming back on to TMS the reason why and you can see we've got symmetry here all of these carbons here and all of these hydrogens are all bonded to the silicon so they're all in the same environment okay so that's why we get this nice strong peak is very rare you're going to get chemicals that you're testing that will have this level of symmetry so that's why we use this chemical okay so let's look at carbon-13 spectroscopy so carbon 13 NMR spectroscopy tells us how many different carbon environments there are in the sample being tested so that's what we're going to look at first so then we'll look at proton NMR later so the peaks on a carbon 13 NMR spectrum they tell us the number of different carbon environments in our molecule okay so it's very straightforward proton NMR tells is a little bit more Q have splitting patterns and etc but we'll look at that later so don't worry too much about that now okay so we have a carbon 13 spectrum here and this is the spectrum of this molecule which is chloro ethane so each carbon in the molecule is in a different environment in this molecule if we'd seen something similar in the previous slide but we had bromine on the end so we know we've got two different environments here and and they have a different amount of electron shielding so for example remember that when we're talking about influence of other atoms this carbon has electrons around it and NMR is only what NMR is doing is it's exciting than nucleon the new clones that are there in the neutral of their in their nucleus in the atom but around the atom we have electrons and that shields the external magnetic field so this chlorine is electronegative so what it's doing is it's pulling electrons away from that carbon in the in the shell there and effectively this carbon is now more exposed to the external magnetic field and as a result then the energy difference is going to be different so the shifts going to be different where is this carbon atom here is further away from this chlorine there will be some electrons Maeby's pulled away from the shielding in there but nowhere near as much as this okay because it's further away from that chlorine so it's not influenced as much so what this does is this transpires into our spectrum so we get ones which are influenced the most are going to be shifted the most because they're going to be affected the most the ones which are further away from the source of influence are not going to be shifted by a smoke so let's have a look so the red carbon this one here okay this is the one that's closest to the electronegative carp chlorine so this one M is going to have the shielding is going to be a lot lower in this carbon because it's been pulled away by the chlorine and so therefore the chemical shift is going to be high and you can see on that graph there on the spectrum that the peak caused by that carbon is a lot higher up now obviously the other peak there and the green one is the one that's not shifted as much it has a lot more shielding in the in the carbon so therefore it's not shifted as much at all now you can see the disease a little peak at zero and so that peak of course is because of TMS okay so make sure you're aware of that it doesn't have to be the biggest peak it just has to be the peak at zero okay okay so carbon 13 legacy the carbon 13 tells us how many different carbon environments and there are um in the sample being tested so and we're going to look at cyclic compounds in particular for this for this example because we look to their aliphatic carbon they're just they're straight chain one so now we can look at cyclic ones they're a little bit more difficult to predict because the cyclic sand they don't have they don't have a straight chain where you can easily identify you know differences in the carbons so this case we're looking for symmetry so here's our molecule here and here's our cyclic compound we've got two chlorines on here and here's the spectrum for it so you can see we've got a lot more Peaks there so what we're looking for is any symmetry in this molecule and we're looking for and you know what what Peaks will this produce so let's go through it so you can see here we have got symmetry straight down the middle there so there's our symmetry so I suggest when you get molecules like this is that you draw your line of symmetry and so in this case it's 1 3 dipolar cycle hexane and then what we do is we look for the number of different carbon environments and we can see here that actually we do have 4 different carbon environments so we have one here so here and we have these ones are in the same environments these ones are in the same environments and this one is in a different environment so so what we're looking for more circle them and see where they are so you can see there's the first one so this is the one that's actually it's a single carbon on its own but actually if you look what's left and right so we've got carbon with the chlorine and a carbon with the chlorine okay and then we've got two carbon hydrogen carbon hydrogen and carbon hydrogen so that one's one environment that's quite unique because it's sandwiched between these two CCL bonds the next two sits these two red ones here these are in the same environment and that's that peak there okay in our spectrum so this is a bigger peak it's much bigger this carbon is shifted quite high cuz it's bonded directly to the chlorine and but also you can see here that these two in the same environment because they're both bonded to chlorine they're both bonded to this carbon in the middle and they're both bonded either side here you can see they kind of there is symmetry there so if we go right across that carbon chain they're exactly the same okay so these two here are different environments so that's this peak there okay so this is these carbons are bonded both of them you can see the symmetry that both bonded to a CCL bond they're both bonded further round to this carbon and they're both bonded to that same carbon there so these ones are actually in the same environment and finally the last one the orange one here is that peak there obviously that's on its own this one at the end here is different to that one because this one is not bonded to a CCL okay this one is bonded to a c CH and the C CH and going around okay so it's as simple as that really it is a bit trickier you've just got to be methodical look for symmetry I find it easier to draw a symmetry line first see if there's any symmetry and then look for your carbon your carbon environments from there obviously that last peak there is TMS as well so no difference you will always get a TMS you'll always get a peak at zero and that's your TMS okay so carbon 13 chemical shifts they have values and carbon environments can be determined okay so this is more of saying you'll be given this data in a day to day data book no more than lady love just have a sheet with this data on and so you will be given this you don't need to actually you don't need to actually remember the information on here but it might not be exactly the same as this and but it'll be something similar okay so you'll have your chemical shifts and you've got your type of carbon environments you can see here what I've done is highlighted the carbons that M is actually causing the shift in red so you can see here there and there and there and there and there so you can see all the way across but from the aromatics of course because that is just carbons but we are and we are highlighting the particular carbon that's actually causing this on your sheet it might just be in bold so that's why you'll find some of them actually in bold okay so what we can do is we can match up the position of the peaks in the spectrum to the table and we can work out what carbon environments exist so it's fine as you know in the different carbon environments but we can actually start to identify what type of you know what could that carbon be next to that's causing it to shift like that so there are some issues though as you you know this is this is science there's always going to be problems and limitations so we've got and a peak at 191 won't will so a peak at 190 will suggest a carbonyl group however we can't be sure if that's not the height of ketone so it's not quite that sophisticated enough to work out exactly what it is and also there are overlaps at peak at 60 and this could be because you got naming or it could be an alcohol or it could be an ester or it could be an ether so there's quite a lot of different possibilities there so I hasn't narrowed it down massively this is why as you'll see coming towards the you know come towards the end of the video we'll look at combined techniques is about using NMR with other machines as well to make sure we can identify the compound that we've got okay so for example let's say a chemical has the formula C 3 H 8 oh and it's spectrum as shown below so what the spectrum there what is the displayed formula okay so that's always being given okay we've been told what its formula is a molecular formula and being given the spectrum and we have to work out what this is so the first thing we have to do is draw down all the possible isomers of c3h8 oh okay once we've got that but you can then start and eliminate then eliminate from them so here they are so here's our 3i Smith so three possible ways in which we can arrange our c3h8 oh so then we have to do is we look at the number of Peaks and you can see in this spectrum we've got three peaks so this means that we must have three different environments so this rules out propound to all as this only has two environments so let's have a look that one there okay so you can see here I've color-coded them but you can see there's only two environments in here so this spectrum cannot be propound to on okay so we have two peaks at 65 and 75 okay and so this suggests that the two carbons are bonded to an electronegative elements such as oxygen okay so this fits the structure of an ether rather than propane one all where we'd only see one peak in this area so we use that data table that we'd seen before or the one that you've got in front of you and we try and say right you know what is these you know the peaks at these values what is actually causing this so you can see here that in this case it is going to be our ether that's the likely structure for this rather than alcohol our primary alcohol okay so that's how you do it you basically just look through now you'll have loads of examples here and the key thing with NMR is practice and practice and practice you know and you'll get the hang of it as good marks in the exam and you just need to be familiar with how you work it out obviously carbon 13 is fairly straightforward relatively speaking to two proton NMR but um you know nonetheless you still need to be vigilant you still need to be looking out for the shift patterns you need to know what the Peaks mean and you need to know obviously you need to know how to identify structure from them as well when you given the molecular formula okay so let's look at the other type of animal which is proton NMR now proton and Mart is a little bit more tricky at this extra features to proton NMR it's a bit like a like an iPhone or suppose hora and you so many galaxies so you've got extra features that are added to this and it has its advantages and it has its disadvantages still it's not perfect so let's have a look at what this is it's a proton NMR spectrum and spectroscopy tells us how many different hydrogen environments we have and and it tells us how many hydrogens we have in that environment so this is good because carbon NMR didn't tell us exactly how many carbons are in that environment it just tells us there are this many environments so proton NMR has got a little bit more detail here okay so so the peaks on a proton NMR spectrum tells us the number of different hydrogen environments okay that's exactly the same as carbon NMR okay so the number of Peaks tells us them of hydrogen environment except we're looking for hydrogen of course okay so we've got our molecule here so this is ethanoic acid in case you've got a carboxylic acid here and we have the NMR spectrum for this here now you can see we've got numbers above the peaks in this spectrum and this tells us the ratio of the areas under the peaks okay and this allows us to work out the relative number of hydrogens in each environments and sometimes these numbers can be decimal so we call this an integration trace this red line so what we do is we measure the area under each peak in the area under the peaks tells us how many hydrogens are in the environment but quite often that could be really really difficult to actually measure the area under the peak so what we do is you'll find in a lot of spectrum NMR machines that I'll actually put numbers above the peaks and that tells you the relative area of that peak relative to you know relative to the smallest peak so this is telling us that this peak has a value of 1 this peak has a value of 3 so this is times we've got a three to one ratio here okay so you can see in ethanol we have two hydrogen environments so we've got one at the end there which is in red and I'm sure the green ones have been circles that's this one here so we have two different hydrogen ions so the number of Peaks tells us the number of hydrogen environments obviously this peak is caused by TMS that's the standard one at the now the peak on the left this one has a value of 1 like I say the peak on the right of the value of 3 so this means there's three hydrogen's in one environment and there's one hydrogen in the other environments there's a three to one ratio and you can see actually this fits with the structure here seen see the green circles here they've got three hydrogens they're all bonded to the same carbon which are then bonded you know further on so they're on the same environment in this hydrogen is on its own it's directly bonded to an oxygen and there's no other hydrogens in here that it's bonded directly to an oxygen so that has its own peak this one shifted well up to the top you know obviously we remember from last time from the carbon NMR this is heavily shifted because look it's literally bonded directly to that oxygen so it's ripping the electrons away from it so it's really exposed to that magnetic field that external magnetic field that's why it's shifted well up to the top of the spectrum okay so I could say that red line is the is the integration trace and it shows the area the area ratio of the peaks is have mentioned before okay okay so just like carbon 13 spectrum you also have proton NMR data as well so it's separate data don't get them mixed up carbon 13 data will have larger numbers on them your proton NMR data has smaller numbers so that's the main difference and and the other difference as well as obviously these are detects and hydrogen environments and not carbon environments but the principles the same we're still using it in the same way so you can see here that all the hydrogen's that are actually being affected in question are the ones are the ones in red so you can see you got an alcohol here at the top here so this is obviously this is the hydrogen that we're talking about and then the other hydrogens in the molecules all the way down this is going to be quite interesting and useful because you'll see when we actually look at you know analyzing spectra this is going to become quite and pivotal in terms of trying to determine that okay so here we've got a spectrum previous spectrum of ethanoic acid okay and we have a peak 11.7 remember and then a peak at two point one so this peak at eleven point seven is actually telling us that it's a it's a hydrogen what's actually causing this peak is this hydrogen that's bonded to the oxygen so that tells us straight away we have a carboxylic acid shifted right up there and then this peak here the one at 2.1 is because of this year so this is telling us you've got a hydrogen it's this hydrogen here that's bonded to a carbon that is bonded to a carbon with a double bond o group on now that would make sense because this double bond o is actually coming from this here okay so if we put the two together it's telling us that we have a hydrogen next to that and actually we know we've got our carbonyl group here so actually that hydrogen is clearly got to be where that R is there okay so that's how you work it out it's just about trying to piece it all together okay so proton NMR spectrum have Peaks that split okay this is where it gets a little bit complicated but it's going to be fine because we'll talk so it will work through it and break it down as simple as simply as you possibly can so this allows us to actually determine the structure now this is immensely powerful for chemists so it's a really good way of determining if we've made a molecule that it's an isomer or if it has isomers you know which I assume is the correct one vital in medicine of course so let's have a look so Peaks that split into smaller Peaks are known as is known as a splitting pattern okay and so the number of smaller Peaks corresponds to the number of hydrogen atoms on the adjacent carbon plus one okay and we call that spin-spin coupling brighter so this is a bit tricky isn't it so this rule is called the n plus one rule okay so let's go through it we'll go through it step by step okay so what we're looking at here remember what we said with proton NMR is it's mainly all about what's the next door to the carbon not their actual or the hydrogen it's not actually what what the hydrogen itself in questions we're always looking about okay what's next door it's it's quite it's quite a nosy M form of spectroscopy so what we're looking for is we get different types of splitting pattern and we call these splitting patterns either singlet doublets triplets quartets okay so basically the peaks that we Sene you've seen one single peak these Peaks can be split into smaller Peaks but you can have more of them so for example a single peak can be split into two or it can be split into three or can be split into four and depending on what it splits in is depending upon what's next door to that okay so let's have a look so a singlet peak what this means for the hydrogen in question that we're looking at a singlet means that we have a hydrogen but that hydrogen is next door to no other hydrogens okay on the neighboring carbon so for example you know that carboxylic acid that we'd seen and we had that lone hydrogen and it was directly bonded to the oxygen that hydrogen would give a singlet peak because it's bonded to an oxygen it's not bonded to a carbon at all and and so therefore that would be a single ER peak okay so that would definitely be singlet a doublet is where we have a hydrogen that is bonded that is so that the hydrogen on the carbon is bonded to another carbon with one other hydrogen on it so that gets us a doublet triplet peak is where we have a hydrogen in question that's that's bonded to the carbon and so that is bonded to a carbon with two hydrogens on there so that could be a ch2 for example and a quartet is where we have three hydrogen's on the neighboring carbon so what we're looking at is what is neighboring it what is next to it so how many hydrogens are next to it and we add 1 so we plus 1 okay so let's have a look at an example it's always easier to look at the example of think so here we've got ethanol okay so ethanol has two carbons and obviously you've got your H group on the on the end there okay so you can see we have three different Peaks here so okay so we've got hydrogen hydrogen and hydrogen okay so you can see in terms of identifying then we have an H peak ch2 peak and a ch3 peak at the top there so the hydrogen on the O H is bonded to the oxygen okay so this is not a carbon okay that's the first criteria if it's not bonded to a carbon straight away that is a singlet peak okay so this is not a carbon so the neighboring hydrogen's is zero so if we apply this n plus one real that's zero because there's no carbon there it's not next to any carbon zero plus one is one that's the singlets so in fact that's what we get we get a singlet peak that's been generated because of the hydrogen on the Oh H okay so let's have a look at another one so the hydrogens on here these ch2s okay so the hydrogens on here are adjacent to one carbon that has three hydrogens on so you can see this here has it next door to an oxygen that's a lot of carbon so we just ignore that so we look to the left of it we've got a carbon there and this carbon has three hydrogens next to it so this means if we apply the n plus one rule three plus one is four so we get a quartet so these hydrogens here will produce a peak and that peak is split into a quartet so that's it there so this quartet is telling us so if we go backwards this is telling is that this ch2 is bonded to something a carbon with three hydrogens on okay and let's have a look at another one so the final one so these three here so the hydrogen's on ch3 are adjacent to one carbon so there it is there's a one carbon and this has two hydrogens on there they are okay so if we apply the n plus one rule we get two plus one equals three and this is a triplet so the peak caused by this one here this one is actually split into three because its neighboring a carbon with two hydrogens on so n plus one so that's the three and you can see there there's your triplet so you can see um how this actually structures and how it works now the key thing with this is just practice because obviously it's all well and good looking in and say yeah you understand it but you know if I was to put an NMR spectrum in front you could you do it and you probably give it a good go if you look through this video and follow the rules and but the key thing is just practice and just get used to practicing with different types of molecules and that's the key thing here obviously this is an alcohol but do it with it but the carboxylic acids do it with an ester and do it with a an amine and a name ID and do it with all these different types and just make sure that you know you're familiar with the types of functional groups in here because that's what's really going to and cause the most influence here is functional groups okay so remember we looked at the integration traces before and and we show this so the integration traces shows the areas under a peak more clearly and what this does that actually helps us to work out that hydroton ratio so they might get you to actually work out or use the integration traces to put the numbers in in the first place okay so let's see how we do it it's pretty straight forward to be honest but when we have split Peaks it's difficult to work out the area under that peak remember because if you have so if you have a quartet how do you then measure the area under that's just too difficult so what the NMR machine will do is it's really helpful as it will put an integration trace in for us and basically what it's doing is its converting the area under that peak into into a height ratio instead so it's converting it into a difference into a different metric so in practice what we do is we use a ruler to measure the vertical parts of the trace and we write the lengths down and use these numbers to come up with the ratio so that's that's basically how we do it I remember good being at uni doing things like this it was a while ago now since I was at university but you know good air going through these sitting down you know and really you know analyzing this is a little bit like a crossword or Sudoku puzzle or something like that so and it's actually quite therapeutic believe me so all you do is you get your spectrum so we didn't learn a mass spectrum but we weren't told the numbers we had to work them out ourselves so this is what this is exactly what I did so in the spectrum and the integration trace shows us a 1 to 1 and a half to 1/2 ratio and so if we round that up to get a whole number we get a 2 to 3 to 3 ratio ok so it keeps it nice and neat so this is our integration trace of a spectrum here and that's basically how we do it and basically what this does is it tells us that we have 3 different hydrogen environments because you've got 3 peaks okay and one with 2 hydrogens in and the other one has the other one has three hydrogens in there so the other two should we say so we've got 2 2 3 2 3 ok now this is really useful because you look at that and you think oh well that's taller than that one it's nothing to do with the height of the peak ok it's very important this has the same number of hydrogens as this one just this one spread over a larger so this red line here whatever line they give you you just measure the vertical parts of it and that tells you obviously the relative ratios okay so let's have a look at some examples here okay so the key thing like to say is practice you know so here we're going to predict the structure of the compound using the dates table from this proton NMR spectrum and this has a molecular formula of c4h8 o - okay now you might straight everything all that's a carboxylic acids um it could be an ester it could be anything like that but least we know the formula okay so it's got two oxygens in and there's our spectrum there and instead of the integration trace we're actually work that out for you already very kind and put the numbers on the top there so it's two three and three so we can see there's three hydrogen environments in the molecule and with a ratio of 2 to 3 to 3 which is likely to be we can speculate but it's likely to be 1 CH 2 + 2 CH 3 molecules within this group okay that's what is like d3 it's always good to get a rough idea and then at least it sharpens our mind a little bit more okay so we're just every time we're narrowing it down to work what it is so this is what we think it could be so we have a peak at four point one which is this one here okay this one at the one to the far left on the side so the peak of four point one has a has a value of two and this suggests a ch2 and if we use the data table so the day at the table that we've got in your in your M D etre sheet then this suggests this type of structure so we have that H there okay and it's telling us that this H is yes it's bonded to a carbon of course it is but this is actually bonded to an oxygen and then next to it is a carbon with a double bond oh okay so that's quite interesting so we've just we've literally glimpsed and a little bit of information we don't have the full structure of course we don't but we know that this hydrogen is next door to this set up here okay so that's giving us a little bit of information there looks quite like an ester doesn't it so the splitting pattern is a quartet okay so what does that mean well that tells us that less this ch2 is actually next door to a carbon with three hydrogens and because it's the n plus one rule so that's likely to be a ch3 molecule so let's move on to the next peak so we've got a little bit of information now we think it's an ester and we think we've got a ch2 molecule bonded right next to that ester group and next door to that is possibly a ch3 so that's what we know already just for one peak so let's carry on because we need to confirm this and make sure we're absolutely correct so we've got a peak at two point one here okay has a value of three which suggests we have a ch3 ch3 that this is the ch3 sorry and use in the data table it's Houseman's we've got this type of structure so this is done as actually we have a ch3 and the hydrogen that's under test is bonded directly to a C double bond o right so this is start to fit together a little bit more so this C double bond o remember we looked in the previous peak we do have a seed or bond o so it's definitely confirming that but actually what this is saying as this hydrogen has bunch of carbon directly bonded to that seed of bond o so that could be this R group here so we could have a ch3 there on the end okay so this is what it's telling us but it's not telling us that we've got this and this that's not what it's telling us it's telling us that we've got a hydrogen next to a C double bond o and that's what we've got here as well so that could be there okay it's very important with NMR not to just add these bits up and get what you you know and work it out it's just telling you what's next to the splitting pattern is a singlet it suggests that this is a ch3 and it's next to a carbon with no hydrogens perfect okay so that's telling us and that this ch3 is next to a carbon and that carbon doesn't have any hydrogens so that's perfect that really does fit that's fitting quite nicely okay so let's have a look at the last peak though this is a peak at one point two as a value of three which suggests that it's a ch3 and we using the data table that we've obviously that you'll have in your you'll have in your data sheet or your data book or whatever you're given actually in the exam it might even be in the exam paper it's doubt it's probably gonna be in your data sheet so and using the data table suggest this structures and our ch3 it's a triplet peak which means it must be next to a carbon with two hydrogen's okay so it's likely to be a ch2 now we've already identified a ch2 here so this ch3 that we're talking about is bonded to another carbon art group so possibly it could be on the end here so we could have a ch3 stuck on the end there next to this ch2 and then we've got a ch3 here on the end okay so let's put all this together so there it is ether a ton of it circling the different Peaks okay so you've got your two there and then you see a ch3 at the end there which is obviously caused by that last peak there okay so make sure once you've drawn your molecule always make sure you test it draw it out and just circle it and see right does that actually fit the spectrum that I've got and if it does the chances are you've got it right yeah well you know more than certain you've got it right again because they're not going to give you anything too horrendous so you can see here that we've got definitely it fits we've got a ch3 bonded directly to that C double bond o group so that was this bit that's what we're telling is about it's got three hydrogens itself which it does that's fine this one's got three hydrogens which is the one at the end it's split into a triplet it tells us it's next door to two hydrogens of carbon went to Hodgins which is fine so this one's a singlet here so that's bonded to a carbon with no other hydrogens that's fine this one is as two hydrogens but it's split into a quartet which tells us it's bonded to something with three hydrogens so you can see here that we do have the three hydrogens so you can see how that's structured but practice practice practice that's the key thing okay so let's look at something else it's a tiny little bit that they've kind of strangely bolted onto and bolted onto the topic there's not a lot of information you need to know about elemental analysis and but elemental analysis is basically just a method which we can determine the structure of the sample under the test and the test okay so very straightforward actually and it looks like this so you won't have one in school or college and if you do it's clearly got a lot of money and so and yeah it's a bit of a kit normally see at university at universities for example have used one myself so there's not you know they're not that fascinating but basically what it does because it helps us to determine the percentage composition of the mass of elements that make that compound okay so fairly straightforward if we know the molecular formula we can actually work out the structure of the compound using a machine like this and basically the data that's produced from the elemental analysis can help us to determine the empirical and molecular formula of a compound as well so your elemental analysis helps us determine the percentage composition of mass of elements that make up that compound so and you might have seen in topic 18 and towards the end that was a big big big topic that one and but right towards the end of the video I'll towards the end and then we look at empirical formula and molecular formula now the figures or the data that we use there was percentage figures so I had a percentage of carbon the percentage by mass of hydrogen etc etc and we use that information to work out in paragraph formula now then percentages of the elements come from this type of analysis here so this is probably the only thing why I think they've kind of put it in here personally I think it should have been in topic 18 where where you had your percentage analysis and the empirical formula because then it would kind of fit but I suppose it's it fits into this topic because it is a spectral technique it's a type of analysis so and yeah so this is basically where it fits but it's just to try and bridge the two so you can see kind of where this odd bit fits into into this but into the specification okay so we're going to look at a thin layer chromatography because remember one of the one of the parts that you are one of the bits in the specification was they had to know about chromatography in different types of chromatography now you would have seen TLC thin layer chromatography and for amino acids so you would have seen it for that section and this was going to look of it in a general form so in case you're thinking hang on have you not done this in a previous topic I have but it was to do with amino acid so we're just going to look at it here in terms of general use rather than just for amino acids so thin layer chromatography it allows us to separate and identify compounds it's quite useful so thin layer chromatography uses a stationary phase of silica or alumina mounted on a glass or metal pate and a pencil line is drawn and drops of mixture are added so you can see here we've got a mobile face here so which is mobile phases the bit that migrates up since the bit that moves and we've got our stationary phase here this is the the phase which doesn't move so in other words our solid silica here so silicon dioxide or aluminium oxide based plates here and then we have a lid on top of this because what we don't want is a solvent to evaporate from our from our beaker we want it to remain in the beaker so what we do is you place the plate in the solvent and the baseline must be above the solvent level so very important that we've got our baseline here with our samples under test on the bottom the solvent line must be below that baseline okay if it's above then you just end up getting your your substances dissolving into the actual solvent and we don't want that do we so leave it until the solvent has moved up near the top of the plate so we just let it rise gently it's soaks into the into the stationary phase and moves up in my grades up and we get a solvent front at the top and we mark where the solvent front is on a chromatogram and we allow it to dry once it's migrated near the top and so then it works really by the mixtures the mixture spots dissolving in the solvent now sometimes these chemicals will actually spend more time added to the stationary phase sometimes they'll spend some chemicals will spend more time in the mobile phase and surf or they'll migrate further up the chromatogram whereas the ones which are not very soluble will spend more time stuck to the stationary phase and therefore will probably sit lower down on the chromatogram okay so we can identify the compare the compounds or the chemicals that make up our mixtures and by checking the positions of them at the end and calculating our F value which is what we're going to look at now so I'd say these can be identified using the RF value from ukata gram and so the number of spots on the plate so when you get your karate gram and it's all dried and finished you'll see there's a few spots in there now the number of spots on that plate basically tells us how many chemicals make the mixture okay so if there's three spots that means you've had three chemicals and that mixture if there's two we've had two chemicals pretty straightforward and and the chemicals these can be identified by calculating the RF value and comparing these to a library of knowing RF values so if we can see here we've got our chromatogram that's already being produced so this is the one that we pulled out of our beaker and you can see we've got a solvent front that's drawn in on the front and we have the distance that's been traveled by our spot which goes and up the top up there so that starts to migrate up and so basically what we're doing so well to work out the RF values you do the distance traveled by the spot which goes up here divided by the distance traveled by the solvent which is this bit here okay we divide them and we get an RF value and what we do for the RF values we compare it with a known library of our values so and that can help us to identify what the compound is depending on what the RF value is however we've got to make sure that we keep certain things constant and keep certain things the same so we get different RF values for different chromatograms so what we've got to make sure is the temperature that this is conducted in remains constant the solvent remains constant and the actual makeup of the TLC plate that remains constant as well so we're got to try and keep things and the same so when we're comparing RF values going to make sure that we're using the same methodology as what the data book is suggesting okay so pretty useful at you so we're separating and we're actually identifying as well now that's all well and good however you can't actually get hold of your sample once it's on the chromatogram once it's on the chromatography paper we can't get that sample back again so there is another method of chromatography where we can actually take our products or products that we've made and we can actually use them they'll do something with it so we can separate them out so gas chromatography is actually a useful method to separate a mixture of liquids that are volatile and hence these can actually be identified as well so very good for volatile substances so a gas chromatography machine again you won't have one of these at school of college they're very expensive bits of equipment they're quite big bits of equipment as well so there's on a large bench and they have this general set up here we're going to go through each one of these sections of the grass of the gas chromatography machine and see what each bit does so in the gas chromatography we have a very thin column that is wound up inside an oven to save space and the column is lined with a solid or viscous liquid such as an oil and this actually acts as the stationary phase obviously that should be an a don't spell station there that with an e so that's it for you looking at pens and pencils so this should be an a so I'll get that changed m so station your face so you can see here here's our very very thin column which is in here very thin column and lines in that column there we have a very like a very thick liquid that's lining in so it is in turn credibly thin wire it's not very thick at all that's like and a bit like fishing wire to an extent so it's a bit like that so this is wound up inside an oven so this is our oven here and this oven is then obviously heats up that keeps the substance inside the tube warm okay so the sample is injected into the machine so there's the injection here so whatever we're using what if we want to sample or separate out we inject it in here and we use an inert gas to carry it so we've got to carry a gas here which actually carries our sample through our column all the way through here this is the mobile phase and is normally something like nitrogen so something inert that isn't going to interfere with our mixture or sample that's under test and so what it does is each substance takes a different amount of time to actually travel through the column okay and it reaches the detector so it comes out and reach the detector and our waste thing comes out on the other side and the length of time it takes it's called the retention time so we put it through here it spends time going through round and round and round and then it comes out and then detect every time it comes out here it detects it and sends a signal to your to your machine which then tells you obviously what Sam then tells you the peaks that are formed and tells us and what the substance possibly could be by comparing with the light people look at that in a moment so the time it takes em for the sample to travel through varies because some molecules spend a lot more time stuck in the the station new phase you can see it correct there so that's the right spellings of the station you face and and some spend more time actually traveling in the mobile phase so if it spends more time in the mobile phase ie the nitrogen or the in any other inert gas then it's going to come through the end of that much quicker some substances like to add ear to the you know the the solid stationary phase within that tube and therefore it's going to take a lot longer to actually a lot longer to actually come through the other end okay and that effectively in itself is a separation technique because we're separating the different components of our mixture but we can also identify it which we're going to look at now okay so let's have a look at the spectra that we actually produce so as you can see it shows Peaks of varying sizes and the appear apps at different times so you can see here we've got our time which at the bottom which is there so that's time in minutes and we've got our detector response and here's our here's our chromatogram here gas chromatography so each peak here each peak in the spectrum represents a different substance and each substance has a different retention time okay so you can see here this is the the distance from 0 to 4 minutes so this is our be tension time retention time here so we can compare that retention time with a library of no N substances to identify and what we could have in our mixture so that's pretty straightforward so the area under the peaks and this tells us the amount of each substance and so the larger that area the more substance we've got so you can see we're a very large area here so whatever this is and we've got a lot of it in our mixture and we've got very little of this here so we haven't got much of this at all and so gas chromatography is actually really useful because it allows us to detect at the amount of alcohol in urine and blood and this can be used in evidence in court because the the results are fairly reliable so this is where gas chromatography is used in things like forensics for example um and also um for I'm art historians or art restorers for example so paint and restorers and so they can also identify volatile compounds and paints such as esters and obviously this is useful for the restoration of the restoration of artwork so what you want to do is try and imitate as close as you possibly can the paints that were used by the original artists if it needed repairing so I'm using and quite detailed chromatograms like this we can actually work out and me but maybes even the age of the painting or even you know if we are restoring it we're trying to you know use the correct you know the correct materials to so it's not obvious obviously you wouldn't use a completely different painter those it look obvious wouldn't it so so yeah so there's loads of different those are different uses for for gas chromatography okay so go look at something called a high-performance liquid chromatography or HPLC now HPLC is used where it's where it may not be suitable to use gas chromatography which is GC so this could be for example a sample it has a really high boiling point or decomposes in heat so for example if it's got a really high boiling point it can't actually be carried through the GC machine also if it decomposes in heat cause remember in in gas chromatography we have an oven in there if that decomposes that's going to be no good because we'd want to know what our sample is and if it's all broken up into different substances and that isn't any good so there is a solution so we used something called HPLC to do this so we have the phases of the mobile station you'll notice in chromatography you always have a mobile and a and a stationary phase so the stationary phase is solid small or small solid particles this could be silica and hydrocarbons and they're in a column and the mobile phase is a polar liquid and so this is things a methanol and water mix so this is the mobile phase these are the different phases that we're going to use in this type of instrument and so the mechanics are that the HPLC solvent is pressurized and we use that in a pump so we've got HPLC pump here and the solvent is pressurized to which the sample and the test is added in the case of this is it here so a sample is other than to the injector and is added and pushed through a column so here's our HPLC column from our sample so we're using pressure here and we're using polar solvents so you can see we're not using heat so this is ideal for things like things which decompose and heat because we're not using any but also the boiling point we're using pressure instead to actually turn it into the phase that we need so we can identify it so each substance just like with GC it takes different amount of time to travel through the column and reach the detector and so this because some again for the same reason some parts will spend more time in the in the stationary phase some will spend more time in the mobile phase and if you spend more time in the mobile phase that's going to come out much quicker out the machine and so therefore the retention time is going to be lower it's not retained in the Machine as long where is obviously if it's stuck on this station new phase for longer it's going to take longer to come through and the station new face sorry the retention time will be longer will be higher so it'll take longer to come through okay so after the sample leaves the column it's now separated and enter the detector part as we can see here so here's the detector section and so what happens is UV light is shown at the sample and the absorptivity is measured here okay so you measure how readily this it's a bit a colorimetry when we looked at as a method for measuring rates of reaction you can use a color limiter and it measures absorptivity so if you remember that and this one is using a similar principle but measuring absorptivity and this information of absorptivity is actually pushed into the into the display the display screen here as you can see and basically speak here is the level of absorptivity which is then read it and obviously into this chromatogram and each peak again represents different substance each one has a different retention times it's exactly the same as UGC spectrum and obviously we can then take that information and we can compare it with a known library of resources and that will help us to identify the substances in our mixture okay so gas chromatography mass spectrometry so GCMs so one what we can actually do is we can combine gas chromatography or HPLC so we can take either of them and we can connect it with a mass spectrometer and we can actually help to identify mixtures in a substance okay so the mixture of substances so this is a substance in the mixture so to say so it works fairly straightforward and so mass spectrometry is actually better use that better use as it's use is much better at identifying compounds via their master charge ratio but analyzing a mixture of compounds is going to be very confusing of course if you put in three or four compounds in a mixture and put it through a mass spectrometer you're gonna get peaks everywhere cuz it wouldn't have a clue what is what remember it's just measuring mass so so what we can do is wrap so we can use a separating techniques such as GC or HPLC and so and we can use that to separate it first which we're going to do because this isn't actually very good both of the methods are not good at identifying what compounds you have in your in your sample okay it's mainly used to separate the substances out yes we can compare against them know a library of resources or ones if you've got a chemical in there that it hasn't already been recorded somewhere so your mass spectrometer is is a better use for that so if we combine these two together we get the benefits of them separating a mixture first into its individual substances and then we can analyze each of them substances separately using a mass spectrometer so it's very powerful tool by combined in the the benefits of both to try and get what we want out of it and so basically the separated compounds run through the MS machine that produces a spectrum to identify each substance so that's what we looked at right at the start of the video when we looked at their mass spectrometer and so the mixture of substances these are fed through the gas chromatography or HPLC machine and this separates them out however instead of detects a net obviously it feeds it straight into the mass spectrometer so they're literally connected to each other and then the substances can then be positively identified as the mass spectra produced can be compared with the line library of no one stored spectra on the other computer so this makes it a really efficient process so actually the user may not even need to actually analyze the spectra it literally just goes through and the computer if it recognizes the spectra that you've just done against the library of known ones then that means it's much much easier to do isn't it okay so this is going to look at the final section and the final section of this video is looking at combine techniques we're taking all of them techniques that we've just seen there and we're going to pull it all together and actually take get some use out of it and they will be expecting you to be able to do this of course in the exam ok so obviously chemists use a variety of different techniques to identify an unknown substance that we're looking for and obviously the skill is putting all of this together using all the different bits of information that we've got from each spectra to try and identify a molecule okay so this is what we're gonna do here so we've got three spectra of an unknown organic compound we're not even going to we're not even known to say what that compound is in terms of its formula so we've just been given a proton NMR spectrum and infrared spectrum and a mass spectrometry spectrum as well so an SMS spectrum so we're going to use all these three to try and identify an unknown compound and we're going to go through them through them one by one if I can get the words out okay so we're gonna look at the ms spectrum first and so this is of our unknown compounds so remember it shows fragments of different M of the compound that we're testing so we molecule is fragmented or broken up into different parts so Intel straightaway remember this is our m+ peak so we have a peak of 58 and so we know that the molecular mass of our substance is 58 straight away so that's what we're looking at there and we also have a fragment peak at 29 okay so this could be due to the CH o or C 2 H 5 it could be either one of them so if we add that up to 29 both of them fragments add up to 29 so that could be a classic sign it could be one of them so we can see from this we can deduce that our mystery molecule has a molecular mass of 58 and may have a CH o group in it okay so it may have something like that in there so may not but it gives us something to hook on to at least but we need a lot more information to actually confirm what this molecule is going to be okay so let's look at our infrared spectrum now so we've got a little bit of information from the mass spec and so infrared spectrum we have a PICUs 1750 centimeter per centimeter and this is likely to be caused by sea oh now you'll have a data sheet with all these with all the spectral Peaks on for infrared so you don't need to worry about that so CO equals R SEO and so from this we can deduce that we either have an aldehyde or ketone an ester an acid chloride or an acid anhydride so I haven't really narrowed it down but at least we know there's a functional group in there that could be one of them now it can't be a carboxylic acid though because the peak doesn't sit between 2500 and 3000 which is exactly where we'd expect to see a carboxylic acid peak and it can't be an amide as we'd see as there's no peak between 3 303 500 so it can't be either by then so we've narrowed it down a little bit and but not not a dramatic amount and like say we need more information to confirm what our molecule is but we know a little bit more about it ok so let's look at our proton NMR spectrum and we're going to use this again to try to find out unknown compound so let's see what we've got three different hydrogen environments so we know that's the structure of this once you know we've got a peak at nine point five and this is due to ACH oh group so that's good because we've we identified that as a possibility for mass spectrometry and there's also Peaks due to CH X group as well and so these are confirmed via infrared so we know and we have CH groups in there definitely because the infrared spectrum shown is that so the peak at one has which is this peak here this one okay so this has an integration of three which suggests a ch3 and there's a triplet which means it's adjacent to a carbon with two hydrogens on it okay so we can see it's got three hydrogens on and it's next door to a carbon with two hydrogens so that could be a ch2 ch3 perhaps okay so the integration peak at two point five which is this peak here okay so that has an integration of two so that suggests its ch2 and it's a pen test which means it's adjacent to M carbons with four hydrogens okay so that's very very important and and so this is likely to be near a ch3 and the CH oh group identified at nine point five okay which itself is a triplet so that one at nine point five is a triplet so this is showing it's possibly bonded to a ch2 group okay so we've got a lot of information there from NMR so the skill is to take all that bits of information then we're going to summarize it here and being able to summarize pull it all together and actually work out art and mystery substance so let's have a look so the mass spectrometer remember told us that our substance must have a molecular mass of 58 okay that's the first bit and I'm infrared spectrum confirms that there is actually a C double bond o group in there so there's definitely that in there however there wasn't any other Peaks to suggest any of the functional group okay so the NMR machine also confirms the C double bond o group so this must be part and that was accorded the NMR machine that was an aldehyde group okay so we know it's now the and so the NMR machine also confirms that we have a ch2 and ch3 group okay which when supported by the mass spectra information and that the molecule had a mass of 58 we can actually start to build I will molecule together so let's have a look so this is a year so it's propane out so you can see we have this has got the mass of 58 we do have our carbonyl group there that's confirmed in the infrared and also if you look at our structure we have a singlet okay that's bonded to our aldehyde group which is [Music] which is fine because that's what we're actually that's what we deduced from that so if I just go back there we are okay so it won't be a single it will it so it would be it would be a triplet because it's bonded to a carbon so we'll just go back there we are that's me not concentrating so this is next door to this is bonded to a carbon which is bonded to two of the hydrogens so that would be a triplet peak of course it's obviously bonded to a carbonyl group was shifted it over to the 9.5 this carbon here has got integration of two but is bonded to three hydrogen's here and also to this side we've got one here so it's got four hydrogens okay so that fits and obviously this one is an integration of three and is showing a triplet a triplet setup because we've got two hydrogen texts or so all that fits okay so it's all about just trying to piece it together get you evidence together and just confirm and just draw a structure and see if it fits that's the key thing I think okay and that's it so that's the end of the video on modern analytical techniques - so you can see there's a lot of information in there and the key thing with NMR is just practice practice practice practice okay and there is a full range this is the last video for four-year - but there's a full range of year 1 and year 2 videos specifically designed for lxl on Alawis chemistry youtube channel and all for free there's whiteboard toriel's on there and there's also exam practice exam technique videos on there as well and they're all very comprehensive or three all I ask is you hit the subscribe button just to show your support and that would be absolutely fantastic and you can also purchase these as well like I say great for revision just click on the link in the description box and but that is it okay bye bye