Organic Chemistry

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18. Reactions of Aromatics:EAS and Beyond

Limitations of Friedel-Crafts Alkyation

Friedel-Crafts Alkylation has several limitations that render it almost useless in the lab. Let's take a look at 4 examples of what these limitations could be.



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in this video, we're going to review some of the major important limitations of Friedel crafts calculations. So it turns out that Friedel crafts calculation isn't all it's cracked up to be. The mechanism was simple. The mechanism makes sense. But it turns out it doesn't work that well. Why? There's actually several reasons. Let's just go into them one by one. The first one is that Well, the first limitation just makes sense. It doesn't react with vinyl or Aral. Hey, lines. Okay, so if you have a halogen directly on a double bond, that Carvell Catalan is gonna be far too unstable. So you're not going to get that reaction to happen? Okay, so here's an example. Let's say that I have a benzene and I'm reacting it with chloral benzene and L c. L three. We would expect that the first step of this mechanism would be that the chlorine bond gives its electrons to the aluminum. And what I wind up getting is a Carvel kata. And that looks like this. What do you think about that car will contain guys. That's a really unstable carbo cattle because it can't resonate anywhere. It's stuck. It's on a double bond. That's one of the worst, most unstable carbo Acadian. So I'm going to say to unstable. Oops. So the answer here is that if you're working with an arrow or vinyl alcohol Hey, lied. No reaction. You're not going to get a reaction with Friedel crafts calculation. Okay, so just the solution would be to avoid these molecules. There's nothing we can do to get around it. Just avoid those. You can't use them. Let's go on to the next, uh, limitation. This one makes sense, guys. Turns out that aniline derivatives are gonna ruin the Lewis acid catalyst. Okay, because if you guys recall, this is the most basic lone pair really possible on Anna Lena. Okay. I'm sorry, Ana. Benzene and Ailes. Seal three is one of the strongest assets. It's a strong Lewis acid. So I guess what's gonna happen. Usually we would expect that the bond between the are between the al Kyohei light would donate to the empty orbital. Correct. But that's not what happens, guys, because it's going to compete with the lone pair from the nitrogen and the analysts actually just gonna complex with it itself. Okay, so you wind up Getting is a ruined molecule because now what you have is here's my benzene. Here's my nitrogen. Here's my age is it's actually gonna be attached directly to the sale. Three. It's gonna make what we call an ad ukt. Okay, but this is a ruined catalyst. Okay, because now it's It's not a catalyst anymore. It just got consumed. Okay, because good luck separating that bond. We've got a positive. We've got a negative. Those things were really attracted to each other. Good luck separating. It's made an ad Acct. It's not separating at all. So the answer here is that if you're trying to run a Friedel Crafts calculation on a benzene, make sure that you avoid an elite at all costs. You cannot use Anna Lean. Um, you know, and Luis Castillo callous. So Thea answer He would actually be the addict. Okay, so it would just be the addict that I showed earlier, but it would not be the right reaction. So would be this thing here. It wouldn't be the correct thing that you're waiting for, which is actually put in our group here. You would not get in our group that would not happen. Okay, so the first thing that you should think is just, like, avoid these things at all costs. But there is another way that you could prevent this from happening if you've already learned about it. Okay, some of you guys have learned about a CIA dilation already through my clutch videos. Some of you haven't. Okay, if you haven't learned about assimilation, don't worry about it. Because that means that I purposely did not teach you that video because your classroom doesn't need it. Okay, But for those of you that did learn the assimilation video, you would understand, Then looking back at that video that a simulation of the aniline would work because what you would do is you would form a nitrogen with a carbon Neil on it, and that nitrogen would not be quite as basic. So this one actually could work. Okay, so if you assimilate it and then reversible e d assimilate it, then that would work. But for the most of you guys, if you did not see that content, then just worry about just ignore it. Because that means you're professor really doesn't care about that way of avoiding, um, the addict. Okay, awesome. That's the second limitation. The first one was You can't use certain ocular. Hey, leads. The second one is don't use anally, okay, there's more. So it turns out that calculation reactions because we learned that our groups are what, their electron donating groups. Right. So remember that our groups are electron donating groups. So since their electron donating groups, they're going toe activate the ring towards further reaction. So when you add that first, our group, it's gonna make it more reactive for the second reaction. Okay, Another thing. Calculation reactions are susceptible to carve okada and rearrangements. Remember that because you form a full cargo Catalan, they could move around. Okay, so this these air just thes limitations are piling up because you're trying to do with synthesis. But you've got all these problems. You've got a rearrangement. You've got extra activity, which we'll talk about why that's important. A second you can't react with Anna lean. So it turns out that the solution for both of these two guys for the activation and for the carbon category arrangements is to a silly instead. Now, guys, what I mean by isolate isn't what I talked about at the top. That's what I mean. What is Friedel Crafts? Ace Elation, right. Friedel crafts. Isolation would be using an acid chloride and, uh, you know, and Lewis Acid Catalyst. Okay, so a silly instead. So how does that work? How does that make sense? Well, let's look at these two examples of calculation versus ace elation and let me show you guys why isolation is better. Okay, well, calculation notice that the intermediate of my of my calculated inner of my calculation reaction is gonna be a Carvel cat. I am r plus. Okay, notice that the intermediate of my isolation is going to be what we call the asili. Um, I on that looks like this. See, Dubon? Oh, plus are Okay, so first of all, are both of these gonna rearrange no guys on Lee? One would rearrange this one has shifts, but this one has no ships, so we can see that if we can use a Soleil shin Ace. Elation is gonna be safer for us to use because we know that isolation. We don't have to worry about shifts. That's the first thing. Okay, Now let's look at the product. What happens when I add these groups. Well, for my benzene ring with the calculation group, I'm going to get in our group. Okay, now, when I add Maya Segal group No. Yeah. My A C L group. Not a group. My A C L group. What I'm gonna wind up getting is a key tone. Okay, What's the difference between both of these in terms of activity? Well, guys, there's a huge difference because notice that this is an electron donating group, but notice that a key tone since it has a partial positive is actually an electron withdrawing group. Okay, so one is an electron. Donating group one is an electron withdrawing group. Why is that important, guys? Because if you add an electron donating group, this is gonna be more activated. And if it's more activated, that means that once it sees another alcohol hey, lied. It's gonna want to react again. And you're gonna wind up getting Polly substitution. You're gonna wind up getting a benzene that not only has one our group, but maybe it has to. Or maybe it has three. Okay, this is bad. I'm just gonna put a sad face. You're gonna get Polly substitution because now you're going to get our groups everywhere and it's difficult to stop. Remember that I told you guys that Tali Lien is 25 times more reactive than benzene. So what do you think? What do you think happens when I have to Tali, Weans or Xilin? Right to our groups, that's even more reactive and more so. It's almost spirals out of control. You can't stop it. It starts adding our groups everywhere. So you start getting sad. You Maybe you shed a tear. Okay, But what happens with electron withdrawing groups, electron withdrawing groups is gonna make it less activated. Right? So what do you think happens when it sees the second A c. Liam Ion doesn't go attack it. I'm gonna take myself out of the screen. No, the answer is this doesn't happen. There's no reaction. So it stays at mono substitution. That makes me happy, guys, because that's what I wanted the whole time. The whole time, I didn't want some mess of Polly substitution. I wanted just one thing on my benzene ring. And that's what I get with Ace elation. Not only that, I'm also happy because I didn't have a rearrangement that messed up my yield. I just got exactly what I was looking for. So now you guys can see you're getting a hint of why isolation is more advantageous to use than calculation. Okay, so now what I wanna do is really drive home. This point of white isolation is better, and we're gonna learn some extra information of how you can use a solution instead of an calculation in pretty much all situations.

Provide the major product and the correct mechanism for the following reaction. 


Provide the major product and the correct mechanism for the following reaction.