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Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

17. Aromaticity



Intro to Aromaticity

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Hey, everyone. Now we're gonna talk about a brand new idea that's actually a huge theme of organic chemistry to, and that's called Air Metis City. So aromatic compounds are compounds that have a really high level of stability relative to their high electron density. Okay, now it turns out that aromatic compounds have their own set of rules that will help us to determine if something is aromatic or not. But for right now, we can generalize to just say that aromatic compounds are molecules that have a lot of double bonds within rings. Okay, now, actually, if you look at my shirt or if you look on top of the clutch logo, you'll see that the clutch logo actually is in aromatic molecule. So these must be pretty badass molecules. Well, let's explore a little further. What makes them so cool? So their high level of unsaturated Now, if you guys remember what the word unsaturated means, it means that everything is not a single bond. It means that you Abdullah Bonds, you have rings stuff that's making hydrogen less, um, prominent on the molecule. Well, whenever you have such a high level of in situation, you would predict that there would be a very high reactivity of that molecule however we find is that molecules that are aromatic are actually extremely un reactive. Okay, so here it says, however, they're difficult to react with. So we find that aromatic molecules actually bucked the trend and are very difficult to make anything happen. Thio. So what I want to do is I want to show you guys in aromatic molecule compared to just a regular double bond to show you just how unusual these molecules are. Well, just you guys know you may or may not know these three reactions. My point here isn't toe bust. Your You know what? It's just to give you an example of the way that benzene and aromatic compounds do not react the same way that double Barnes dio. So this first reaction here, I'm not sure if you guys remember was called Hydro Halogen nation. Okay, you can find more information about all of these reactions in the addition chapter of your textbook. So Hydrology nation was a reaction that added a hydrogen and a halogen across the double bond. So we would expect is that you would get in h and an ex added to the total bond. Well, guess what happens when you react? H X with a benzene. Back in the old days in the 18 hundreds, scientists predicted that we would wind up getting three. Hello, Jin's reacting because you have three double bonds. But it turns out that's not what happens. In fact, the answer would be no reaction. Why is that? That's peculiar. Let's look at the next one. This next reaction is called Halogen Nation. This is another very, very common edition reaction. And in halogen nation, what we got was die. Hey, lied. So we would actually get an anti die. Hey, lied. Now if you look at a benzene ring, which, by the way, I already said it a few times. But this is called a benzene ring, right? If you look at a benzene ring, has three double bonds. You might think that you're gonna get X is everywhere on every single carbon. But in fact, the answer again remains no reaction. Why is that? Thes told Bonds look like they should be reacting. Why are they not reacting? It's so confusing. Let's look another example. This one's a bit more tricky. You might not remember it. What happens when you're at K M N 04 at zero degrees temperature. So this is Ah, cold reaction of communal four. You got it. This would be a one to sin. Dial's reaction. I know you said it. I got you. So one to sin dials. So you would wind up getting hydroxyl groups that air sin to each other. Okay, so you might think that if we react this reaction with benzene, surely you're going to get alcohol's everywhere. But let me just step out of the camera really quick. You guys guessed it. No reaction. Why is that? It's so weird. Okay, well, that is exactly the question that tons of scientists were competing to answer back in the 18 thirties 18 fifties. There. So confused. Why is this happening? And they finally realized it's because of a phenomenon called Arum Metis ity. Okay, So before we can really learn what the criterias of domesticity are, we learned need to learn about the categories of air Metis City because it turns out that there's different categories of aromatics. Let's go over these really quick. So first of all, is just the standard idea of Air Metis City, which I already explained. And air Metis City says that these compounds are gonna display unusually high level of stability. Okay, so this is just what I was just describing in the above reactions. Okay, Now there's another concept called Let me just get another color here. Non aromatic. Okay, so we have aromatic and we have non aromatic, Non aromatic compounds are compounds that don't display any unique level of stability or instability. Basically, non aromatic compounds are normal molecules, the kinds of molecules that we've discussed in every chapter previous to this one. So if you think about any molecule that we've reacted with in the past, that would be non aromatic. It would just mean that it's normal. Okay, but then we've got this third category that you've definitely never interacted with before, and that's called anti aromatic. Okay, now, you might not understand why something is anti aromatic, but for right now, I want you to know that it's going to be a compound that displays an unusually low level of stability. So these molecules are actually very reactive. In fact, they're almost impossible to make scientists spend years making these anti aromatic molecules because they're so reactive that they're unstable and they decompose on their own. Okay, so we're talking about crazy level of instability here. So here's an example, Guys, what I've done here is I've given you three trying thes air three molecules that have three double bonds a piece. Okay. And what we find is that their structures aren't that different. One of them has a ring. Actually, two of them have rings. One of them is a straight chain, but actually they're stability. Ease are off the wall. Different because anti aromatic, we said, Is that stable or unstable? Unstable. Anti aromatic is gonna be super difficult to synthesize. It barely even lasts at room temperature. Okay, then we have non aromatic, non aromatic is just normal. I would just be a normal a cule that we would have discussed at a previous chapter Normal stability. And then finally we have aromatic, which is just this bad ass idea that we're gonna introduce and that we're going to continue to talk about in the next coming videos. And these air very stable, Very cool molecules. So I'm going ahead and putting greater than signs to show that stability increases as you move up this spectrum. Okay, so now you guys understand kind of the differences between the types of air Metis ity, but we're gonna need to learn a lot more and really dive into this idea before we can understand what separates an aromatic molecule from a non aromatic molecule to an anti aromatic molecule. So let's go ahead and move on to the next video so we can get a better idea of what is it exactly that separates these molecules and makes them so different?