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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.

Table of contents
18. Reactions of Aromatics:EAS and Beyond

Benzene Reactions

We know about EAS but did you know there are actually many reactions that fall under this category? 


EAS Reactions Overview

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in this video, I'm going to introduce all the different reactions that can occur to benzene through an E A s mechanism. So, as previously discussed, benzene is going to require very strong electro files in order to react through E. A s. And some of these re agents are going to require catalysts in order to become strong enough for the bending to react with them. So let's just take the first one into account e s halogen nation. So halogen nation would be a reaction with a double bond and a diatonic halogen. So something like X two, okay, but actually, X two is not a reactive enough Electra file to react with the benzene. So guess what. If you just put X two in a mixture of benzene, you're not going anywhere. You're not gonna make a substituted benzene. So how do we get the X two to react? We need a catalyst, guys, and this is gonna be a Lewis acid catalyst. F E x three. Okay, now, this is gonna work for Broening. I'm gonna put here where X is equal to specifically bro Ming or chlorine. And you always want to make sure that when you're performing one of these s hallucinations that you're using the same halogen in your catalyst as you are in the actual electro file. And that's gonna become important later when you look into the mechanism. As you can see, the product is now gonna be a mono halogen aided benzene, which is great. That's what we wanted. Okay, Now it's important to distinguish this mechanism from another reaction we learned in the past just called halogen Nation. So it's important that when you discuss this mechanism, you call it E. A s hallucination because specifically, this is the one that requires a Lewis acid catalyst. All right, so let's move on to the next one. It turns out that I A donation is a little bit tricky. Iodine does not. I was gonna use a different color. Let's use red. So iodine does not react with the Lewis acid catalyst, um, of iron and three ha logins to perform this e s reaction. So we're gonna have to use nitric acid instead. H n 03 Okay, so that's one little peculiar thing. You have to memorize that I a nation in order, put an iodine into benzene we're gonna need to use nitric acid, Not our Iron Lewis acid catalyst. Okay, let's move on. So the next time you wanna discuss is nitrate Asian Now, a nitro group is not a group that we've discussed. Ah, whole lot at this point of the course. So I do want to just help you guys understand what a Nitro group is by drawing it, it would be something like this. We have a nitrogen with a double bond. Oh, and a single bond. Oh, and there's gonna be formal charges, right? The single bond. It Oh, has a negative charge. The positive. I'm sorry, the nitrogen, since as four bonds as a positive, but notice that this has no net charge because they cancel out. Okay, So that's why when you draw no to you, draw it neutral without charges. Even though those charges to exist now, there are two different ways. Toe add a nitro group to a benzene. But they're really the same thing. It's just that different, you know, different websites, different textbooks, different professors like to use different combinations. So the most common would be using nitric acid, h n 03 and sulfuric acid. okay. Ah, combination of sulfuric acid and nitric acid is going to react together to make the active Electra file, as we will see later when we go into the mechanism. Okay, but just keep in mind that you could also generate this Elektra file just through using concentrated h N Okay, we're really in the first example. You have one acid directing with another. When you use concentrated a Channel three, it just reacts by itself. One a Channel three molecule rex with another one and makes that active Electra files. So regardless of how you you know how you draw it, it's really gonna produce the same product. Okay, so a b e a s nitrate Asian Also, One thing to keep in mind is that nitric acid can also be written differently. It can be written as ho no to Okay, this is just a little like, you know, little technicality that actually could make you guys stumble on an exam because you might not, you know, be recognizing it as horno too. But it's the same compound as nitric acid. H N 03 just written different. It's basically written on the connectivity in a condensed structure instead of just based on the molecular formula. Okay, so let's go on to Sulfa Nation, which is actually going to be the kind of most special reaction we're gonna talk about on this page. Because sulfur nation is the only one with these two arrows. Let's discuss what that is. Well, first of all, the product of sulfur nation is gonna make what we call a Seoul phonic acid group. Okay, so that's what we have at the top. And by the way, guys, I forgot to write with the product of nutrition. Would be it would be a nitro group. Right? So you got nitro. And we've got so phonic acid, these air literally functional groups that we just learned in this course. Okay, so, phonic acid. Now, the way that we do a sulfa nation is to use sulfuric acid. So h two so four and s sulfur try oxide. Okay, now it turns out that when you heat up H two s 04 it's gonna actually make the sulfur trioxide the eso three. So sometimes it's just written as fuming. H two s 04 Okay, However you see, it That's fine as long as you have fuming. H two. So four or h two So four eso three. It's the same thing. It just means that it's actually fuming. It's it's evolving in eso three gas That's going to react. Okay, No, that's gonna make your soul phonic passes. Okay, Now, when you want to reverse it, if you want to do go into reverse reaction, that would actually be called a diesel for nation, okay? Or E a s diesel finish in and to diesel. Funny, it's actually even easier. You're just going to use a dilute form of the assets so you might see it written as dilute h two so four or because the fact that really it's usually heat that winds up taking the so phonic acid group off. You might even see it written as just steam. Okay, because steam can be used to basically take off the soul phonic acid group and reverse it back to benzene. So again, I'm writing in multiple ways so that you're not getting you're not gonna get stumped on an exam or on like an online homework. There's different ways Thio represent these reactions, but they're all really the same thing. Steam dilute h two. So four, they're all gonna that would take it towards the diesel for nation back to original benzene. Okay, Awesome. So now let's work on the Friedel crafts reactions and the Friedel crafts reactions are ways to make our groups or put our groups onto a benzene. Now, guys, this is gonna be very important because any time that you can add in our group toe a smaller molecule that's really important for organic synthesis. Aromatic compounds are extremely important for all kinds of pharmaceuticals. And if you can add our groups and make them bigger, that's awesome. You know, you could make a million bucks making the next Viagra. So anyway, so let's go ahead and talk about calculation and ace elation. So calculation would be the reaction of an alcohol. Hey, lied. So the Rx okay with a Lewis acid catalyst. Okay. And that Lewis s a catalyst for Friedel crafts reactions is gonna be an aluminum catalyst. So it's gonna be a l X three once again, X is really equal toe Onley, bromine and chlorine in these cases, and you wanna use the same X in both of them as we're going to see in the catalyst, it might actually matter. Okay, so we want to go ahead and use the same X in both. But typically, guys, the one we're using is chlorine. Okay, so for the rest of you know, the reactions that I work with you guys, I'm always gonna be working with alcohol. Three, it's the most common version. Okay, now, what we see is that the X actually doesn't end up on the benzene. Right? What ends up on the benzene is the our group. Okay, So just keep in mind that the our group is what stays. Whatever you have is an art group, and then you're gonna get some kind of acid by products. Okay, then we use we have Friedel crafts, ace elation, Friedel crafts, ace elation would use an acid chloride. Okay, Now, on acid chloride, if you're not familiar with it, is a functional group that we're going to use a lot in organic chemistry to, and we're going to react it over that same Lewis acid catalyst in this case, a l. C. L three. Because we're using a chlorine, and that's going to give us actually what we call in a sealed group. Okay, so calculation gives us an alcohol group, literally, just in our group. Whereas ace elation gives us an a social group. So a carbon, you'll group a key tone. Okay. Usually a key tone. All right, so those are the two Friedel crafts reactions. They have a lot of similarities between them. As you can see, they use the same re agents or the same Louis eyes and catalyst. But there are some differences that will explore later. Finally, we have any Carvel cat ion. So what's the big deal with this? Well, carbo cat ions, by definition, are super strong electro files because they have an empty P orbital. They literally you're saying feed me electrons. So any reaction that you've ever learned that involves Carvel, Catalans could theoretically work with benzene. Now we're not gonna have to go back. And, like, remember every single Carvel cattle intermediate reaction. But there are two different combinations that I want you to focus on. Okay? And that would be one thes air. Very common. One combination would be H f and the double bond. Okay. When you have HF in a Taliban like for example, cyclo beauty mean Okay, that could generate a carvell Canada, because you're gonna get in addition, reaction. You're gonna wind up getting a Carvel Catalan on the square on the cycle of butane. And then that one's of getting attacked by the benzene. Another combination that can produce Carvel Catalans would be actually be f three. So a strong lewis acid with alcohol. Okay, so we're gonna see later how BF three and alcohol can also produce carbon Catalan like structures that will react with benzene and produce in our group. The whole point here is at the end that we're adding some kind of our group tour benzene ring. Okay. Some professors and text might even refer to these as Friedel crafts reactions, but I prefer to discuss more of their mechanism and highlight the fact that they are Carvel cat and intermediate reactions. So you can really instead of trying to remember how that's a Friedel crafts, think of it more just as a Carvel cat and reaction that will, you know, basically tempt to the benzene to react with it. Alright, so hope that makes sense so far, let's move on to the exact mechanisms off E A s reactions

Great job, guys! I know that was a lot. Now we will move on to break down each one of the reactions mentioned above.