Organic Chemistry

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18. Reactions of Aromatics:EAS and Beyond

EAS:Any Carbocation Mechanism

This next group of EAS Reactions is grouped together because they share a common active electrophile: a carbocation. Popular carbocations include those catalyzed by hydrofluoric acid and promoted by boron trifluoride



Any Carbocation

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Now we're gonna talk about another category of E s mechanisms that are all related in one very important way, which is that they use Carvel Catalans as their active Electra files. So I'm just gonna call this category that any Carvel Catalan category of e s mechanisms. So, as you guys know, pretty much any reaction that you learned from organic chemistry one or two that can generate Carvel cat ions could be used in an E s because the benzene could attack the Carvel Catalan immediately when it sees it. However, we're really just gonna focus on the two most common ways that we see this because I don't want you guys to spend rack your brains trying to remember 15 different reactions. These are the ones that come up the most often. Okay? And they're the ones that air catalyzed by H f Hydrofluoric acid or promoted by boron. Try fluoride. Okay, as I said earlier, obviously, this entire category is defined by carbon cat ions. So you have tow watch out for carbo cat ion ships, right? Awesome for rearrangements. Okay, guys. So how did these occur? Basically, there's two main ways that we find these um, a double bond with H f is gonna wind up yielding a positive charge because it's in addition, reaction that positive charge contracted the benzene. Another popular way that we see these reactions work is alcohols and boron. Try fluoride. Okay, It's also very strong Lewis acid catalysts. And as we'll see what the mechanism, it makes sense how it makes a Carvel cat ion. So let's first look at the H f mechanism. And guys just, you know, I'm gonna be skipping the drawing of the Sigma complex for these because it's literally the same thing as Friedel crafts calculation. So the first step of this mechanism is gonna be that my double bond attacks the Electra Filic h. The reason that ages, Electra Philip Guys, is because remember, there's a very strong dipole making a partial negative and a partial positive so that double bond is attracted to the hydrogen. That's going to give me an intermediate that looks like this. I'm now gonna have an extra h on one side, so two ages because I already had one prior. But I'm gonna have a positive charge on the other. Okay, now, this carbo Catalan would not shift in this specific situation, but you do have to be concerned about shifts in general. So definitely make sure that you take you take care of that before you would ever react with a bending. Now, what we're used to seeing in a typical reaction in or go one is that the flooring would attack. Okay, this would be called a hydro halogen nation reaction. Okay, you would get the f attacking, and that would be it would be the end of the reaction to get alcohol. Hey, lied. What do you think is gonna happen here? Does that happen? No. Guys, what's gonna happen is that the benzene is going to compete with the fluoride to be the nuclear file, and the bending is gonna win. Okay, We're gonna get a very high yield of benzene attacking the Carvell Canada instead of flooring. And after all of your, um, after all of your resonance structures, you get something. It looks like this age. A cycle beauty group. Um, double bond. Double bond. Positive. Okay. What do you think we can use as the conjugate to make the elimination reaction take place? You could use the f negative, right? so the F negative could come in and do the elimination step. And what do we get? We get in our group? So here's my benzene. Here's my our group. In this case, it's a cycle beautiful group plus notice. I get h f at the end. So that means that this Hydrofluoric acid was a true catalyst because it's regenerated at the end of the reaction. So, guys, I hope you this concede this is the same thing. Israel Craft calculation is just with another set of reactions or another set of re agents. Okay, now let's look at an alcohol with BF three. OK, what's gonna happen here, guys, is that BF three once again is a very strong Lewis acid. It's got that empty P orbital. Okay, so the bond between the carbon and the oxygen can easily break and donate its electrons to the to the orbit. Okay, Now, obviously, what that means is that it's the oxygen is picking up its electrons and giving them to the boron, but we're just gonna draw it all in one step. What that's going to give us is it's gonna give us a carbon cat. I am plus be F three with an O. H. Negative. Okay, so now you know what's gonna happen. We've got this positive charge now, remember, it could rest. I mean, it can't resonate. That's wrong. It could rearrange. So just be mindful that in this case it won't. But if, for example, I had a metal group over here, you know that it would wind doing a one to shift. But, you know, let's just say now the benzene reacts with it. Um, I'm gonna wind up getting a benzene ring that after drawing my Sigma complex, it's gonna look like this H and once again, cyclo beautiful. And now what do you guys think is gonna be the conjugate that reacts with the H And actually, this one's a little bit tricky. You guys were right. I know that You guys are saying that negative charge, but it's a little bit tricky because what winds up actually reacting is actually one of the EFS. It's gonna be f be f to ohh and would actually be would actually winds up being more reactive. Is that one of these efs is going to do the elimination now. Why is that important? It's not really that important, but let me just show you something that's very interesting about this, Which is that now you get your same cycle beauty group. But now what are byproducts? Well, now I'm actually getting h f, even though it didn't start off with any HF. I get it. And I'm also getting now b f 20 h. Okay, so this is this is the only part that's worth mentioning. Guys, do you think that BF three is a true catalyst in this case? Would we call it a catalyst? No, because it actually noticed it actually is being consumed. It actually is a reactant that changes at the end of the product at the end of the reaction. So we would say that this is a reaction that is promoted by BF three not catalyzed because it actually is consumed in the reaction. So you have to say that it's promoted. It's an acid promoted reaction, not an acid catalyzed reaction. All right, but other than that, this is a Friedel crafts calculation in every other sense of the word. You've got your Carvel Catalan, and you've got your final calculated benzene. Okay, so I hope that made sense. Guys, let's move on to the next video