This is just a quick little video to address a subset of functional groups that you might not usually think of as related. These functional groups are all going to be what we call concealed functional groups because they don't show up in IR. Let's go ahead and talk about these and why exactly that happens and what they look like. These groups are as follows. We've got alkyl halides, ethers, and tertiary amines. These groups, even though they really seem like they have nothing to do with each other, they actually have something really big in common which is that you're not going to see these in the functional group region. They have no absorptions in the functional group region. Why is that? Well, because remember that in order to have an absorption in the functional group region, you need basically three different things. One of three things. You either need a double bond, or you need a triple bond, or you need some kind of bond to hydrogen.
So now we look at these three and what we wonder is, well, what kind of bonds do they have? What we're going to notice is that they all have CH sp3 bonds. So all of them have that. You really pretty much every single molecule in the world is going to have that. But then besides that, what else do they have? Well, one has CX, another has CO, and the last has CN. What's kind of the common theme here? None of these extra bonds are going to result because these are all fingerprint bonds. These are all bonds that would show up below 1500. That means that when I draw the IR for these molecules, what are they going to look like on IR? These molecules are all going to look like alkanes because the only bond that they have to H happens to be the alkane, not anything else. Nothing else has a bond to H. The only reason I'm going to see these things at all, there's going to be any absorption, has to do with the H's over here. It doesn't have to do with the functional group at all. That means that these three functional groups are going to be imperceivable from alkanes. You're going to need to use other clues to figure out if you have them.
Let's just go ahead and draw this really quick. That means that I would expect that the spectra for these guys is literally going to look just like an alkane and that's it. Nothing else. It might as well it could have been well, I don't want to do that. It could have been cyclobutane or something. It could have just been an alkane. But it happens to be an alkyl halide or it happens to be an ether, you're never going to tell an IR. That's another limitation of IR that IR doesn't do a great job of picking out these different functional groups that don't show up in the functional group region.
Now I mean a quick note that some professors might say that you can use the fingerprint region to tell if you have these molecules or not. The truth is it's complicated. The truth is it's not as straightforward as they might say. Most courses in organic chemistry are not going to cover that. That's why like I said, I'm ignoring the fingerprint region. But for right now, we're just going to assume that you can't see these functional groups on an IR spectrum. I hope that made sense, guys. Let me know if you have any questions. Let's move on to the next topic.