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18. Reactions of Aromatics:EAS and Beyond

Electron Withdrawing Groups

18. Reactions of Aromatics:EAS and Beyond

Electron Withdrawing Groups

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Adding a single group to a benzene ring is the first step. Now, what happens if we want to do a second reaction on that benzene. Where is it going to add? This is the question we will be answering.

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Activity and Directing Effects

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Now we know how to add a single substitue in tow, a benzene ring using an e s mechanism. And we're pretty good at figuring out how to add different types. You know how to add nitro owes and our groups and key tones. But now the question I have to ask ourselves is what happens if you want to do a second reaction on that benzene? So what if you already have something there and now you're adding Ah, second E s regent? Where is it gonna add? How is it gonna add? How is that first substitute going to affect the second? It turns out that it really has a huge effect on the second one. And that brings us to the es off mono substituted benzene. So we're not talking about just regular benzene. We're talking about benzene with a substitution already. Okay, this section also is called directing groups or activity of benzene. Okay, so all of that is covered in this section. Okay, so it turns out that that first substitue int is gonna really alter the election density of the benzene ring. So it's going to affect the reactivity towards subsequent reactions. And it's going to affect the direction of subsequent reactions. Okay, so let's look, the first thing that is going to do it's gonna affect activity. Okay, so it turns out that we have to be This is our first introduction to these terms of electron donating groups or electron withdrawing groups. Okay. Thes are extremely important principles in organic chemistry. And they're gonna come up not only for the rest of this course, but also for the rest of your professional career. If you're want to go into anything pre health and you need to take more classes in the sciences and in the life sciences, then you're gonna need to know about electron donating groups and electron withdrawing groups. Okay, So it turns out that first of all, if that first subsidiary that you add happens to be an electron donating group, that means it's giving more electrons to the benzene do that's gonna make it more reactive or less reactive towards another e A. S reaction. Remember, the benzene acts as a nuclear file in the reaction. So the more electrons you pump into it, the more you're gonna activated to react. So they activate the ring towards more reactions. Okay, so if you add an electron donating group, it's gonna want to react even more the second time. However, if you had an electron withdrawing group that's gonna pull electrons inside out of the ring, making it less nuclear Filic. So it's gonna deactivate. Oops. That's not how you spell it. Deactivate the ring towards future reactions. Okay, so that means the second reaction will be more difficult to perform than the first meaning. It's actually less reactive than benzene by itself. Right? But that's not it. Guys and you every morning. Well, Johnny, how do I know if something's electron donating? We'll get there. Okay. Just hold on. Okay. So also, guys, they have directing effects because it turns out that electron donating groups tend to be what we call Ortho. Oh, pera directors. They tend to direct towards the Ortho and pair of positions, whereas electron withdrawing groups tend to be meta directors, meaning that they direct subsequent um, e s reactions toe happen on Lee at the meta positions. Okay, so here I have a picture of these two ben zines and an electron donating group. We would expect toe add the second s Regent in the Ortho positions or in the pair of positions. Hence Opie, Director. It actually means that it directs all of those positions. Okay, Whereas many directors electron withdrawing groups, right, they pull electrons out of the ring, so they're gonna tend to add in the meta positions. Okay, I forgot to draw the Dye poll of the electron donating is gonna push electrons into the ring. It directs towards Opie, whereas electron withdrawing groups direct towards the meta positions. Now, the scientific explanation of why that happens is gonna be for another video. We're not going to really talk about the scientific technical definition right now. It has to do with residents structures. But, you know, you could you know, you could also read your text book. If you want more information on that, What I'm gonna focus on for right now is really just memorizing and really just knowing which groups or your electron donating and which groups are electron withdrawing. So let's move on to the chart. That's gonna help us with this information.

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Badass Activity Chart

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and this brings us to wait for it the bad ass E a s activity chart. So this chart is gonna be the go to that you can use toe, learn what groups are electron donating an electron withdrawing. And also, if they're gonna be Ortho Pere or metta directors in regards t A s. So, first of all, let's just learn how to, like, navigate this chart. There's two major lines that you need Thio understand? Here one that's the activity line and the other one is the director line. Okay, Now the activity line is really just comparing to that of an unsubs itude, benzene. So we're saying is that any group that is above that line above that arrow is going toe activate towards further es more than regular benzene. Any group that's less than that line is gonna deactivated. So as you can see, that's the first set of arrows going up and down the second group or the second arrow is the director arrow on. The Director Arrow says that anything that's above that line is gonna be an Ortho Parra director, and anything that's below that line is going to be a meta director okay. And as you can see, there's a general trend that the activators tend to be Ortho pere. The D activators tend to be meta with basically one noted exception, and we'll get there in a second. So now, before we're talking about the individual groups, let's also talk about some generalizations we can make. Well, it turns out that electron donating groups all have something in common, which is that they give electrons to the benzene. And how do they do that? Well, first of all, anything with a negative charge is electron donating. So just keep that in mind. Electron donated by definition of a negative charge. It's gonna be giving electrons away. But you can also have, um, you know, basically donated effects by one just being in our group. Remember that our groups, through a phenomenon called hyper conjugation, can share some of their electron density with the benzene. So remember that that has to do. That's the same principle that stabilizes Carvel cat ions. The more our groups, the more stable of Carvel Catalan. Same thing happens with benzene ring. The more our groups, the more donating is So this effect is from hyper conjugation okay, But the other way that you could donate electrons is through a lone pair, which I've drawn here. So in electron don't in your group could just be any group that has a lone pair right next to the ring. And that would be through resonance because that lone pair could answer the ring through resonance structures and it would spend a lot of its time in the ring. Okay, so that's the general features of electron donating groups. And even if you don't remember a single group here, we're going to go through the groups one by one. But even if you don't remember a single group, you could use that trend to know. Hey, is this electron donating? You could just look at it and tell. Okay, now we've got our electron withdrawing groups. The generalization we can make about electron withdrawing groups is that they have a positive charge. So obviously anything with a full positive charge right outside the benzene ring is gonna pull electrons towards it and deactivate it. But also, this goes for partial charges. So anything that has ah, partial positive charge is going to deactivate the ring. Okay, so a really easy example. This would be carbon eels, right? Carbon eels have a partial positive and a partial negative due to die polls. Right. So if you have a carbon carbon right next to benzene ring, that partial positive is gonna pull electrons away. So again, even if you don't remember a single group here, you could use that pattern to deduce. Is this gonna be electron donating or electron withdrawing? It's really a simple is positive and negative. Okay, Now, what I want to do is get into the specific groups that you need to memorize and the order that they're in, because the order is actually gonna be important for a lot of reasons in this course. Okay, like I told you earlier, electron donating electron withdrawing groups are some of the most popular concepts in organic chemistry too. So you definitely want to be familiar with them. Okay, so we said that anything that's above the line off benzene or reactivity is gonna be more reactive than Benzie. And that definitely holds the case. So for example, in our group, Okay, that's that would be called. Let's just say it was a metal group that would be called tall Ewing, right? So if that was tall Ewing So ch three. Okay, this is just an example. Halloween is 20 times 25 times more reactive than benzene, so you can see that it's definitely ah good on activator, because the fact that it's gonna make bending 24 times more likely to react in an e s reaction. Well, as we go up the spectrum, they're just gonna get more and more activating from there. In fact, if you might look in your textbook, your textbook might have some information about these. But when you get up to, like an O. R group, so here you have no with a lone pair that was attached to a our group, that would be 10,000 times more active, so you can see that it really starts to add up. Okay, so these activating groups definitely make it more reactive. On the other hand, we know that the first one was from I'm sorry. We know the first one is from hyper conjugation. The second one sense as a lone pairs from resonance. On the other hand, if you go down the list, anything below that line is gonna be less active once you get all the way to Nitro Nitro is probably the most deactivating group and nitro is gonna be It's It's like too many zeros. It's like one out of 1000 times, so basically one over 100,000 times less reactive than bending so nitrate Asians are actually gonna require, like, very strong acids in order to proceed and heat because they're very, very inactive. Okay, so you guys can just see how this works. It's kind of a spectrum. These numbers are not for you to memorize, just for you to kind of conceptualize understand that the further we go up, the more active it is. Okay, well, it turns out that in general we can split these up into different categories of activity. Okay, with anything close to the line being what we call weekly activating our weekly deactivating. So we would say that our groups are weekly activating and you want to say Johnny 25 times doesn't sound like it's weekly. It sounds like it's strongly activating, remember, compared to 10,000 times, it's pretty weak. Okay, so weekly activating. Then we would say that basically Angeline and fennel and everything you know that has a lone pair directly touched a hetero atom that's gonna be strongly activating. And then we've got hetero atoms next to carbon eels. These are moderately activating. Okay? And the idea here is that. Think about it, guys. The weekly activating one is just because of hyper conjugation donating a little bit of its electron density. The strongly activating ones, like nitrogen and oxygen with a lone pair. Those are strongly activated because they're donating their entire lone pairs of the ring is basically resonating. Okay, why would this Carbonell compound be moderately activating? Well, it can still donate its electrons. Okay, so this electron pair is still going to donate, but it also has a di pull pulling away. Right? So it kinda cancels out and makes it moderately activating. That's gonna be important later when we look at the differences between Anna Lean and then other types of aniline derivatives. Okay, so you guys can see that basically, you make the activity go down a little bit by adding that carbon. Kneel next to it. Okay, Now, let's look, On the other hand, we have these three categories where halogen are actually weekly deactivating Okay, We're gonna see how that's important in a second. So halogen, our weekly deactivating. Then we have carbon eels that are moderately deactivating. And that pretty much applies to any carbon Neil. So that would be, um, in Esther and Amad Key tone, whatever. It's gonna moderately deactivating. And I'm actually gonna take myself out of the screen here so you guys can draw behind me. But as you guys can see these groups nitro, um, sel, phonic acid and a try halogen aided carbon those air all gonna be what we consider just a second sorry. These air all strongly deactivating. And the reason that they're strongly guys is because you've got extremely strong partial positives there. In the case of Nitro, you have a full positive. So it really doesn't get more deactivating than that because you have a full positive charge. Carbon eels, on the other hand, are you know, our weekly are moderately. I'm gonna come back in, are moderately because they don't have quite a strong of a partial positive. And then finally halogen are deactivating slightly just because of a typo. They have They have a typo pulling out of the ring. Okay, So now you guys kind of understand the spectrum here in general. Guys, you can say that nitrobenzene is the most deactivated benzene. And in general, you can say that Anna lean. So that would be a nitro. A nitrogen with two hydrogen and alone pair on a benzene ring. Angeline would be the most activated because it's the one that's up here. Okay, you might be wondering, Johnny, but what if you have hydrogen or are groups? Whatever this whole notation, the reason I voted as n lone pair and a lone pair is I'm saying, guys, I don't care what's on the rest of the atom. I don't care if it's carbons or whatever. What have you? I just care that at least has one lone pair as long as has a least one lone pair. It can donate to the ring, and it can contribute through resonance, and it can activate it. Does that make sense now? Also, guys, the order that I put them is is important. Nitrogen is more basic than oxygen, so it makes sense that nitrogen is lone. Pair is gonna be able to donate to the ring more than oxygen. So just remember that Angeline is a little bit better than female. And then both of those would be better than a carbon ill with hetero atom next to it. Okay, so that would be if you have a carbon deal with head or autumn next to the benzene ring, that header autumn will donate its electrons will be moderately activating. Okay, so now we understand the differences between the activators and the D activators on the badass activity chart. One last thing. Guys, we wanna talk about this exception here. So in general, we can say that Opie directors are activators rop directors and the activators or many directors. But we have this one exception of halogen. Okay, guys, this is just something that you're gonna have to memorize. That halogen, our weekly deactivating. But they're actually Ortho para directors. Okay? It's probably much easier for you to memorize it than to fully be able to draw it out and understand it. That's what I'm gonna recommend for now. Just remember that halogen are the one exception to the rule where they're actually deactivating the ring, making it less reactive, but they prefer toe. Add the second reaction in the Ortho and pair of positions. Okay, guys. So I hope you like the badass chart will be coming back to this many times this semester when we have to talk about electron donating groups and electron withdrawing groups. And this border free agents is somewhat important. I would I would ask you to definitely try to start understanding and comprehending the differences between these, you know, a soon as possible. All right, so let's move on to the next video.

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Predict the major product of the following EAS reaction.

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Predict the product of the following multi-step synthesis.

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