16. Conjugated Systems
Like the Cope rearrangment, Claisen can be differentiated from other pericyclic reactions due to its lack of conjugation as well. So how will we distinguish the two? Well, unlike Cope which uses only hydrocarbons, the Claisen Rearrangement utilizes a very specific functional group. Let's take a look.
Definition of Claisen Rearrangement
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Hey, everyone. In this video, we're going to discuss a specific type of Sigma Tropic shift called Take Laysan rearrangement. So that is what is the place and rearrangement? Well, it's a heat activated. He activated 33 Sigma Tropic Shift that involves in a will, either. So that's interesting. It's a specific type of Sigma Tropic ship that's a 33 but specifically the reactant needs toe have an owl ether in the original functional group to then transform into a placement arrangement. If you don't have that aval ether, you're sunk. It's not gonna be a place entry arrangement. Okay, um, I will go ahead and help you identify the alley through in a second, but let me just read through a few more points first about it. So, depending on how many Perisic quick reactions you've had toe learn at this point, you might be like, kind of confused. How do I identify which type is which? Well, something that's easy about the clay sin is that it's one of the few perry cyclic reactions that does not begin with any form of conjugation. So notice that we have a dying here, right? But these this dying is considered to be isolated because it's not next to each other, right? So it's really the Onley Perisic of reaction that could possibly take place between an isolated dying with an aloe ether. If you think about it with those two things in mind, you can easily determined this is gonna be a place and rearrangement. Now, something else to keep in mind is that right now I've drawn this molecule very nicely. So it's very easy to kind of think mechanistic Lee how it would form into this product because the old bonds air close to each other. But just you know, the way your professor or your homework may give you the problem, it may require some Sigma Bond rotation for you to get it toe. Look in it toe look nice and orderly before you do your mechanism. So I'll show you a few examples later about how we're gonna have to rotate it first into position before we can, then draw the mechanism. Okay, cool. So let's go ahead and just identify. First of all, what do I mean by Allah Ether? So, guys, an aloe ether is like, I mean, let's just go all the way back to the beginning. What's an ether? And ether is an R O. Our group roar I'm in ether and specifically an aloe ether would mean that your oh is attached to a CH two that's then attached to a double bond. Okay, so that's what an aloe group is. This is it. This this group right here would be alot. You should be familiar with a low positions by now because we use them a lot in organic chemistry, but it means you're not directly attached the job on your one carbon away. So what is the aloe ether in the original product? It's actually this. I'm sorry and I met reacting in the original reactant. It's this thing. The other thing on the top is actually part of a vinyl ether, and that part actually could change. There are clasing rearrangements that happened with vinyl ethers. There are placing arrangements that happened with fennel ethers. So don't you shouldn't worry too much about the top part, because that part could change based on the specific type of place in, but the bottom part that alot part always has to be there always needs an ally either So that's why that's like the one defining characteristic off a place and rearrangement. Now, once again, guys, you guys should already be familiar with how the number, um, Sigma Tropic shifts in general. But remember that it has to do with the bond that is being broken and the bond that is being made. So in this case, the bond that is obviously broken is the one between the ones. Because you can see over here it no longer exists. The bond that's being formed is the one between the threes, because now that's a new bond over here. So we would then say that this is in the category of a 33 Sigma Tropic shift because a new bond has been created between the threes quote and lastly, what would this mechanism look like in general terms? It would just be any mechanism you can draw. That's Paris cyclic and concerted. That is, um, going to create a bond and break upon. So what I would do is something like this, something like this on something like that. Cool. And there you have it. That is your final product. Now, guys, it turns out that it can get a little bit more complicated than this, though. And that's because sometimes in your final product, you're gonna end up with having thio decide which totem ER is the most favorite. Because if you'll notice we actually have a carbon. Neil, we have a carbon Neil as our end product here. Okay, we have a carbon deal and something that we learned about carbon eels. Ah, long time ago, or, I mean, you've definitely come across it at some point in organic chemistry is that carbon eels are able to tot, um, arise into Enel's, so they're able to tot, um, rise into Enel's. And this is so this is called the Keto, and this is called the Enel. Now, most of the time, the keto is favorite almost all the time. The kiddos favorites so usually don't need toe worry about it. Usually, you could just leave the product the way it is because Kato's air favorite But some specific molecules prefer the Enel. So what that means is that when you come across a molecule that favors the Enel position, you must talk to rise to the Enel in the last step. If you don't itemize the Enel. You get the question wrong because you picked the wrong totem. Er, Okay, So what it says here is that in the final Todd Memorization Final, Todd immunization step is required for molecules in which the Enel form his favorite again. Not too many molecules favor the final form, but if they do, you must taught him rise to the anal. Makes sense. Cool. So what we're gonna do in the next practice in the next example is I'm going to remind you guys with some of the properties of Keto, you know, ta terrorism, and we're going to pick the most favored one equilibrium.
When is Enol Tautomer Favored?
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Alright. So here are two products of place and rearrangements. Now you're gonna have to kind of trust me on that because we didn't go through the whole mechanism, but just kind of take my word for it that this is the product of the place and rearrangement, which actually is the product we just did. And then this is another place and rearrangement. Okay? So just take my word for it that these are two products of place and rearrangements Now we need to do shouldn't have circled. Good thing having Eraser. What we have to do is pick the more stable Todd More of the two using what we know about Keto, you know, top in old Todd terrorism. Now, if you're confused about this or if this isn't too clear to you, I have a whole series of videos on picking the most stable ta tumors in Todd memorization. So you can just search in the search bar of clutch Todd memorization, and you're gonna get more information on this. This is just a quick review. And remember that. So let's just look at the first. We'll do both of them side by side. So the first one. This is my Keto. And this is my eagle. Right? Which one is favored in this case? So, guys, just so you know, the rule is that the Keto is pretty much always favored. So I'm gonna go ahead and circle it. We're done. You would not taught. Memorize this one. Cool. What about this equilibrium here? I'm going to step outside so you can see both. Clearly what I see is that here, once again I have a Keto. And here I haven't seen only now out of these two, which one is more favored? Guys, there are only two examples in which the Enel is more favorite and I'm going to give them to you Here. One is when you can make an aromatic product or an aromatic Enel. And two is when you have a beta die carbon Neil, you know? Okay, Thes air. The two situations in which en als are actually more favored. If you have, if you can either make it aromatic or if it's in the form of a beta die. Carbonell and I do go over both of these situations in my top memorization videos. So what do we have here Do we have any of those two situations? Yeah, we do, because notice that our first molecules not not aromatic, aromatic, just means that has all training single and double bonds, which is gonna make it more stable, like our clutch look like a benzene ring. So this one does not look like a benzene ring. It's not aromatic, but this one has a benzene ring. It's actually female. The specific Enel is called Penal, so if you have a choice between non aromatic and aromatic, we picked this one. So it turns out that this molecule, if you do not totem, arise to the final. You get the question wrong. So this is the one specific situation or one of two situations that you have to make sure that you taught him rise to the Enel. If it's stable, if it's more stable, but the other one, you could just leave a keto. Does that make sense? This is just to do the guys. This has to do with the fact that we're using oxygen now, and oxygen has the ability to either form and alcohol or either form of carbon deal. So that's why you have to think about this step with a place and rearrangement. Okay, awesome. So let's move on to the next video
Predict the Product
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provide the mechanism and final products for the following reaction. You may skip the Todd memorization mechanism if one is required. Cool. So, first of all, what are we even dealing with here? Well, all I really see for sure is that I do have an aloe ether here, so I have an aloe ether. Another thing I noticed is that my double bond is not conjugated with any other double bonds, so I'm just gonna put here. It's not conjugated and I'm reacting with heat. So what this tells me is that this must be a place in rearrangement, which, specifically, remember, a clasing arrangement can be more technically defined as a three comma three place an arrangement that is gonna help us determine which bonds to make which bonds to break. So just, you know, guys like common sense tells you it's a place in because it's on the place in topic. But I'm trying to help you think, coach you through how you would see this if it was in the middle of 40 other reactions on your exam. That's how you would distinguish that. This this must be a place in. Okay, cool. So what else do we need to do? We must rearrange this because And that's the only mean, not rearrange. We must rotate and then we can rearrange. We must rotate because we need the dull wants to face each other. So in this case, what we're gonna do is we're just gonna rotate this guy up, so let's read, Draw it down, are here. Oh, and now let's put the double bond right here and now we actually can start to visualize thes two double bonds coming together and making a single bond in between them. This is the way you would rotate it so you could visualize the place and rearrangement. Now, something else to just, um to be aware of guys, is that remember that I told you that the bottom part of the al ether always stays the same, but the top part might change. So this is an example of the top part is different than the other example did. The other example was a vinyl ether, but specifically, the top part is what we call it fennel ether, not phenol. Phenol is different. Fennel either because directly, one which is fine, too, because we can we can use that bulb on inside of the aromatic ring to do our mechanism. Cool. So, guys, um what's gonna happen? Remember, this is a 33 clasing rearrangement, and we have toe break upon and make a bond may be the most obvious. One is the bond that we're gonna make. We know that we have to make a new bond here because that's the only area that's missing a gap, which means that this is the three and this is the three. That being said, that means we can count backwards and figure out with one positions were This is my two. And this is my one. This is my two. And this is my one and guys. What this means is that I am now ready to break bonds and make bonds using my mechanism. So what I would do is move my let's say my electrons here and then move these electrons here and then move these electrons here. And what that's going to do is it's gonna give me a new structure that looks like this. So this appears to now be a carbon hell. This is now a single bond. This is now a single bond. This is No one double bond. That metal group is still there, and these old bonds didn't change. And there you have it. We just broke the bond in between the ones. And then we made a new bond in between the threes and we just did a placement rearrangement. Cool sorrow. Are you guys happy? Makes sense. Did I miss anything? Guys, I missed something. We're not done yet because this happens to be the one unique type of totem er that prefers to be Enel because it wants to be aromatic and turn into a penal with an O. H. So that means that if you it says you may skip the top memorization mechanism was one is required. But I still need to write that it's gonna totem rise. So let's go ahead and do this with equilibrium. Arrows. Let's write totem arise. Just so you guys know in this question, it says you can skip it. But almost all professors in all textbooks will not make you draw the top memorization step for this reaction, because it's not the point of this reaction. We have a whole chapter about Todd memorization chemistry that you can you can learn about that mechanism if you want. But the point of this, this is Perry. Cyclic reaction is just to understand the top memorization will take place. So my final final product would be this with double bond, Double bond, double bond. Ohh! And then single bond. Single bond. Dull bond. Methyl group. Cool. And you don't have to draw it just like that. You could also have drawn it sticking out. And that also would have been fine. Cool. And there you have it. Guys, We are done with the place and condensation mechanism. Alright, great. I'm sorry. I said placing conversation and I met place and rearrangement. Okay, Awesome guys, let's move on to the next video.