 So, we've looked at a number of different spectroscopic techniques in order to analyze the structure of simple organic compounds, but this is the final one that we want to look at in terms of infrared spectroscopy. And hopefully by the time we've got this one under our belts, we should be able to look at data from all these different types of outputs and use different pieces of information to help us put together the identities of some of these organic compounds. You will have noticed for some of these techniques that they can be a little ambiguous, they can give us some information, but not necessarily all of the information that we need. And so the best case scenario is for us to actually start to put some of these bits of evidence together to help us to build a picture of exactly what sort of molecules we are looking at. So as with so many of the other types of spectroscopy that we've looked at before, what we do with infrared spectroscopy is we fire in electromagnetic radiation at our molecules and we see what happens in terms of the absorption of that particular type of EMR. As far as the infrared region of the electromagnetic spectrum is concerned, the absorbance is affected by the type of bonds that occur within a molecule and the types of atoms that are attached to that bond or by the bond. Covalent bonds that are hit by infrared radiation vibrate depending on the strength of the bond and the mass of the atoms. And we have all these kinds of wiggling, twisting, stretching effects that occur as a result of that. So the infrared radiation that is being absorbed by the molecule is causing molecules to wiggle, to stretch, to bend, to scissor. It's not important that you know exactly what's going on in each of these situations. What is important is that depending on what happens, that can change the output and therefore that can give us a little bit of information about the nature of the bonds and the types of atoms that are attached as a result. And so again, as we've looked at previously with all these different types of spectroscopy, what we are interested in is not so much a deep understanding of how each of these techniques works, but more how we can use the data in order to identify the identity of different types of organic compounds. So let's look at some output. The one that I guess you're always going to be looking for first is the OH group. And the hydroxyl group occurs in a region of the infrared spectra, which can confuse it with certain other types of bonds. But the hydroxyl group always stands out because it's a very broad trough. And you may remember that I've previously talked about the fact that sometimes when we look at the output from these spectroscopy techniques, we're actually looking at troughs rather than peaks. Sometimes we'll get peaks, which is telling us about the absorbance. Sometimes we get troughs, which is also telling us about the amount that's absorbed or about the amount that's been transmitted. So therefore, if we look at 100% being transmitted as our baseline and then moving away from that, if some of that is absorbed, that means that not the full 100% will actually pass through. And so that's how we create these troughs. And you will see troughs in IR output as you'll see in the next slide. The amine group are the little vampire fangs. So if you look at two sharp peaks, as opposed to the broad peak or trough that we saw for the hydroxyl group, that's telling you about an amine. A knockout fang is the secondary amine. And secondary amines occur exactly the same as secondary alcohols. That means that they're attached to a carbon that is attached to two other carbons. There's also a terminal alkyne, which is another way of getting this little knockout thing. And then there's the hairy beard, which is a sign for the carboxylic acid. Now, it's probably good in terms of, as with most of the tricks that you use to help you identify what you're looking for, it's useful for you to keep that. It's not necessarily useful for you to talk about the smooth tongue or the hairy beard when you're identifying your different functional groups in an exam. But just make sure that you identify where those are located. The particular shape that tells you that it is a carboxylic acid or it is an alcohol. And that we can, and usually using that sort of data, we can go from there to construct some evidence for what it is that we've concluded is the identity of the molecule.