Organic Chemistry

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16. Conjugated Systems

Cope Rearrangement

Ready to learn a specific type of sigmatropic shift? The cope rearrangement can be differentiated from other pericyclic reactions due to its lack of conjugation



Definition of Cope Rearrangement

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Hey, guys, In this video, I'm going to go over a specific type of Sigma Tropic Shift that's called a cope rearrangement. So what is the co pre arrangement? Well, it's a heat activated 33 Sigma Tropic shift that involves on Lee hydrocarbons. Okay, so it's a specific type of 33 psychotropic shift that involves Onley Hydrocarbons mean you can't have oxygen involved, no hetero atoms. And I just want to remind you that this means that all the rules of Paris cyclic reactions still apply. This is concerted. It's non ionic. It's reversible, all of that. But on top of that, it just happens to be a very specific subset of Sigma Tropic shift. Okay, Now you, depending on how many Paris cyclic reactions you've had to learn this point, you might have a lot of different actions in your head. It really depends on how much your professors putting on you right now if they want you to just know cope if they want, you know a bunch of them. But I'm here to tell you that it's actually very easy to distinguish the co pre arrangement from a lot of other different types of Perry cyclic reactions because this is one of the few that happens without any conjugation at all. Notice that my first molecule, the thing that I'm starting with is not conjugated. This is not a typical dying. This is. I mean, it's a dying, but it's an isolated dying. It's not a conjugated dying. So when you see this type of rearrangement happening and it doesn't have a conjugated beginning point, the beginning point is not conjugated and it's hydrocarbons. You know that it's a cooperation. So I'm just trying to give you some clarity and how to think about recognizing this. Okay, also, just so you guys know this molecule the starting react, it may require some rotation to visualize the 33 location, meaning that right now I have it very conveniently aligned for you. So it's very easy to visualize, but sometimes your homework or your professor could give it to you in a way that's like linear, and you're gonna have to kind of rotate it yourself to visualize what the resulting mechanism would look like. Okay, cool. So why is it called the 33? Let's just go over this one more time. We have a bond breaking here between the ones. We have a bond that's making that's being formed between the threes. So if you count it around, that means that you're forming a new bond between the 33 Once again, this is hydrocarbons on Lee, so it's called a cooperate arrangement. Also, I just want to remind you guys of the mechanism the mechanism would just be something there multiple ways you could draw it, but just something that makes sense where you're breaking a bond and you're making the new bonds. So what I would draw is something like this. Cool, awesome. So that being said, let's go ahead and do this example, so provide the mechanism and final product for the following reaction. So notice here, guys that I'm given an isolated dying that's Onley hydrocarbons. But it's not lined up in a way that's easy for me to react because it's written out in a linear structure. So that means, like I said before, I could even decide what this is. Let's try rotating it so they can face each other, and so we can get a better idea of what we're looking at. So I'm gonna try to do here and maybe in maybe this space right here. Is it going to redraw the molecule in such a way so that I can see what it looks like? So let's go ahead and draw it. This could just be a circle, actually, let's just draw it anyway. Cool. And then what I'm gonna draw is I'm gonna draw this toll bond facing the same direction, but then everything else wrapping underneath it. So I'm gonna put this single bond here Now, instead of the next Taliban going up, I'm gonna draw it down. Instead of the next one going off to the left. I'm going off to the right. I'm gonna put it to the left. And then there appears to you one more double bond that I could face this way. Cool. And now I have something that I can look at. In fact, I drew it too small. I mean, Aiken, you can work with it, but let's make it a little bigger, so it's easier to look at cool. Awesome. So now that we have this molecule that's rotated correctly, we can think Is this like what type of reaction is this? Well, it's not conjugated. It's an isolated dying. So there are really no other Perry cyclic reactions that could happen here. It has to be a Sigma Tropic shift and specifically there on Lehigh hydrocarbons involved. So this looks like it's gonna be a copra arrangement, which is a 33 So let's go ahead and, um, draw the mechanism and then provide the product. So the mechanism would be that I break the bond and make a new double bond. Then this told, one comes and I make a new single one, and then this one comes around as well. So what this is going to give me is a new compound that looks like this where now, at the bottom, what I have is a double bond here, a single bond here, a single bond here and a double bond here. Cool. Just so you know it, the final product here is actually the same exact product that we started with. Okay, um because the fact that this is a very it happened to be a very simple co pre arrangement where there were not a lot of substitue INTs, So the end product turned out to be the same exact thing that we started off with. That's totally fine. That happens with Sigma Tree. A big shift sometimes. So just so you know, just to you are aware, if you ever get the same product, be sure to be careful. But it's OK that happens with Sigma Tropic Shifts sometimes. Okay, so that is our product. And once again, we already know it's a co pre arrangement. But if we had to name it, the way we would name it is by counting. This is the one. This is the two, and this is the three. And then realizing this is gonna be a 33 cope rearrangement. Awesome. So that's it for this concept. An example. Let's see if you guys could do the practice. Problem yourselves.

Provide the mechanism and final product for the following reaction