We finished off with this slide here, where we were going through some example spectra to illustrate the chemical shift and how the The actual environment in which the particular nucleus sits can determine its chemical shift value. And also, we didn't consider this that much, but sorry. You can, what we call there integrate each of these peaks in NMR spectroscopy, because integrate gives you the size, the area, under the peak, and the area under the peak, is for proton NMR at any rate, is directly proportional to the number of protons. So that's quite a useful way, also, of assigning peaks in an NMR spectra to particular positions in addition to the chemical shift. So this was examples, and a bit like infrared spectroscopy, what you can do now is an analytical technique is you can use NMR to assign particular groups within a molecule. So say you have an unknown compound, you want to know which groups are present. People now have tabulated, as we see in this slide here, ranges in which certain characteristic chemical groups have chemical shift values. So there's a summary offered on this particular slide here, and you can see that something like a carboxylic acid proton has a very high value of the chemical shift. And remember that means that it's in the case quite de-shielded. And also you have the aldehidic proton here, that's also quite de-sheilded. So it's got a high value again. Again these are all measured PPM as we said in the last day's lecture, they're measured relative to the standard which is usually tetramethylsilane, and then you can see if you have an aromatic compound. You expect those protons to resonate in this range of chemical shifts. So you can see that the NMR spectroscopers can run as NMR spectrum, work out what the chemical shifts of his or her particular compound is, and then based on a graph like this, he or she can have a good idea of what kind of particular group is present in the molecule. So again, in terms of analytic spectroscopy, again, you would use a range of techniques. You would use what we call elemental analysis to work out what actual atoms are in a molecule. Then you would run perhaps a UV spectrum, and that would give you some more information. Then you might run an infrared spectrum, and that will give you more information, and then you can run an NMR spectrum as well, and that gives you a bit more information about the molecule. So that's how you analyze molecular structure using spectroscopic techniques. And again the analysis of spectra, like we said as infrared spectra is more an art than a science. And clearly, it's a case of getting very experienced in the analysis of spectra. So, if you're an NMR spectroscopist, you'll be doing this every day. So, you're going to be able to work out the actual group quite easily. So, it's a little bit confusing in the beginning, and you have some examples in the workshop today. But, what you've got to remember at this stage is the main thing is to try and get the basic theory right about NMR, try and get why the cause of the magnetic field is shielded by the electrons, giving us a chemical shift. And also we're moving on today to another aspect today called spin, spin, splitting, get an idea of what the basic tier behind that is as well. And as I say, then you'll have a chance to analyze some spectra. But in terms of being a good analyst it's experience more than anything else that comes into play.
