Cope Rearrangement

Hey guys. In this video I'm going to go over a specific type of sigmatropic shift, that's called a cope Rearrangement. So, what is the cope Rearrangement? Well, it's a heat-activated 3, 3 sigmatropic shift that involves only hydrocarbons, okay? So, it's a specific type of 3, 3 sigmatropic shift that involves only hydrocarbons, meaning you can't have oxygen involve, no hetero atoms and I just want to remind you that this means that all the rules of pericyclic reactions still apply, this is concerned, 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 Sigmatropic shifts, okay? Now, depending on how many pericyclic reactions you've had to learn at this point you might have a lot of different reactions in your head, it really depends on how much your professor is putting on you right now, if they want you to just know cope, or if they want you to know a bunch of them, but I'm here to tell you that it's actually very easy to distinguish the cope Rearrangement from a lot of other different types of pericyclic 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 diene, this is, I mean it's designed it's an isolated diene, it's not a conjugated diene. 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 cope rearrangement. So, I'm just trying to give you some clarity in how to think about recognizing this, okay? Also, just so you guys know, this molecule, the starting reactant may require some rotation to visualize the 3, 3 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 going to have to kind of rotate yourself to visualize what the resulting mechanism would look like, okay? Cool.

So, why is it called a 3, 3 , 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 3, 3, once again, this is hydrocarbons only. So, it's called a, cope rearrangement, also I just want to remind you guys of the mechanism, the mechanism would just be something, there are multiple ways you could draw it but just something that makes sense where you're breaking a bond and you're making a new bond. 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 diene that's only 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 can even decide what this is let's try rotating it. So, they can face each other and so you can get a better idea of what we're looking at. So, what we're going to try to do here and maybe in, maybe this space right here is I'm 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 can just be a circle, actually let's just draw it anyway, cool? And then what I'm going to draw is I'm going to draw this double bond facing the same direction but then everything else wrapping underneath it. So, I'm going to put this single bond here. Now, instead of the next double bond up and then I draw it down, instead of the next one going like off to the left, I'm going to off to the right and put it to the left, and then there appear to be one more double bonds I can face this way, cool. And now I have something to make them look at, in fact I drew it too small, I mean, I can, 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, but what type of reaction is this? Well, it's not conjugated it's an isolated diene. So, there are really no other pericyclic reactions that could happen here, it has to be a Sigmatropic shift, and specifically it's their only hydrocarbons involved. So, this looks like it's going to be a cope rearrangement, which is a 3, 3. So, let's go ahead and 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 whole bond comes and I make a new single bond and then this one comes around as well. So, what this is going to give me is a new compound that looks like this, we're 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, the final product here is actually the same exact product that we started with, okay? Because of like, this is a very, it happened to be a very simple cope rearrangement, where there were not a lot of substituents, so the end product turned out to be the same exact thing that we started off with, that's totally fine, that happens with Sigmatropic shift sometimes. So, just so you know just so you are aware, if you ever get the same product, be sure to be careful but it's okay, that happens with Sigmatropic shift sometimes, okay? So, that is our product and once again, we already know it's a cope rearrangement 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 going to be a 3, 3 cope rearrangement. Awesome. So, that's it for this a concept and example, let's see if you guys can do the practice problem yourselves.