So we're done, starting out, we refer back to our electromagnetic spectrum, we talked about on the first day. We said it goes from high energy regions you have the gamma rays and the x-rays, then we come down to the UV and then the visible, so we've talked about how you use UV visible spectroscopy. And then, we come down into the infrared region that's just below the visible region. And now, we're going to talk about a region off the electromagnetic spectrum. That's the low energy still that stays in the radio wave region. And that's the frequencies [COUGH] at which you observe magnetic resonance transitions from nuclei. So we're talking about nuclear magnetic resonance, NMR spectroscopy. So again, we're gonna do it the same way. We're gonna look at, rather than just trying to assign spectra and looking at them, at this level of education, you should know what's the underlying theory, or at least some of the underlying theory, of why you have such a phenomenon. And [COUGH] what you need to know is that the nuclei of certain atoms has a property called spin, so nuclear spin. Sorry. Just let me go back here. My pen. So we got nuclear spin and what that, well, let's move on to, yeah. So what you've got to think about, I mean it's one way of thinking about it, it's not exactly the right way of thinking about it. Is that you have the nucleus, what makes up the nucleus, the protons and the neutrons is rotating. What it ultimately has, what every fundamental particle electron has a spin and the proton has a spin, is called angular momentum and it's a fundamental property of the particle. People like to say it's spinning. But it's actually not. It's just like say something has a color. What we have to accept is that certain fundamental particles have the property called angular momentum. And in the world that we understand, the real world, we associate angular momentum with something spinning, rotating. So we can picture this if we want to, to try to understand this. The best way is picture it as the nucleus. It's spinning, like the Earth's spinning here. So as I just pointed, I used this caution because it spins really, it's a purely, again all this comes from quantum theory. So any spinning object has an angular momentum. So that's what the nucleus has. It's got angular momentum. But it's not due to active spinning, it's just an inherent property of the nucleus. So then, because it's a quantum theory phenomenon, you can't have any value of the angle momentum. So here you have a carousel, it can go at any speed spinning around. That's the angle momentum. But when you have the angle momentum in these nuclei or electrons, then, they're only permitted certain values, certain speeds. So when we say the nuclear spin is quantized, and the spin or the angular momentum can have only fixed values, so that's the first thing. The angular momentum that has only got fixed values. It can't have any value if angular momentum. And then again, [COUGH] going back to the analogy of something rotating. You're gonna guess only particular speeds of rotation are possible. So the angular momentum is quantized. You probably get that. So now, we have the nuclear spin. And what we see here is the spin is characterized by this what we call a quantum number, I. And depending on the particular nucleus we're looking at, it will have different values of this spin quantum number, I. And here, I've just given a series of the rules of why these different nuclei, they're just broad rules. You can decide whether it's an integer, like this one here. The deuterium or its half integer, as 3/2. You can have 5/2 as well, 7/2 for some nuclei. So the general rules are, if you have even mass nuclei, so composed of even numbers of protons and neutrons. Now, they have zero spin. So we're talking about the most common nucleus in organic or biological molecules, carbon-12. That's got zero spin, so that's got zero angle of momentum. And also 16 oxygen, oxygen-16 has got 0 spin. So I = 0 for these. But nuclei with even number of protons and odd number of neutrons have a half integer spin. Well, the proton is an unusual case. The proton, the hydrogen, has a spin of a half. I equals a half. And also carbon-13 has a spin of a half. And 31 phosphorus has a spin of a half. And then, you have some nuclei with odd numbers of protons and neutrons. Have integer spin values. So here you have the deuterium nucleus that's got one proton and one neutron. And that's got an integer spin of one. Another example that's important in Biology is nitrogen-14. That's got seven protons, the number seven, and seven neutrons. So again, most likely to turn it's gonna spend up one. So these are the broad rules. Why this is the 3/2, why this is a half, it gets a bit more involved. But these are the general rules. So the thing is some nuclei, especially pretty important ones here, have got null spin. And what that results, we're talking about spectrocity. Move on to this. What I mean is that you won't get any spectra due to these nuclei anymore. So that's the span, [COUGH] and the important part about this span is that, what it generates in the mark is it generates a magnet. It makes the nucleus like a magnet, in the magnetic field. Again, it goes back to physics. So we can imagine the nucleus is rotating and we know that the charge nucleus is a plus one charge. So if you have a rotating charge, what that does is it generates a magnetic moment, behaves like a magnet. So if you have spin on the nucleus, when you put it in a magnetic field it will try to align itself with the magnetic field. So it'll only have a magnetic moment if I is greater than 0. So carbon-12 and oxygen-16 has I at 0, so it's got no magnetic moment. But if it's I greater than 0 like the proton, I is equal to a half, then it generates a magnetic field. Like a magnet. So this is just a graphic representation, so here you have your protons, again, we're trying to use this analogy of spinning around, so it's got a North Pole and a South Pole, so it behaves like a little magnet. And then, what's important is the magnetic moment is proportional to the spin. So we saw the proton has a spin and a half and therefore the magnetic moments were proportional to that, so another nucleus, I think we had boron-11, had a spin of 3 over 2, so that would have a larger magnetic moment. So in the absence of an [COUGH] external magnetic field, just like any magnet, then it doesn't, it'll be random you're it, this position in space, and put a magnet there and you have no magnetic field around it. Then it will, you can put it in any orientation. But if you put a magnet near it, then it will try to orient itself in a favoring direction. So here, we have a magnetic field. Here, we have our bar magnets. North and South Poles. [COUGH] He puts it in stamagmas. It will try to line up like that in the magmas. Now, what we have here is a spinning magnet. We said this is rotating around. And it's slightly different, the way it behaves in the magnetic field, in that, rather than just lying up, like the bar magnet did over here, it'll tend to spin. It will tend to rotate around in the magnetic field. Its like a gyroscope, so here we have a gyroscope, if it started spinning it will process around the gravitational field and here we have a spinning, or the analogy is a spinning nucleus. And when you put that in the magnetic field, it won't line up, but it will precess around like the gyroscope. So the key, I know this sounds probably all very strange and new, is [COUGH] the procession then around, how fast that processes around, will be determined by the strength of the field. So if you have a very weak field it will process around at a certain rate, then you increase the size of the field it will process around even quicker.
