in this video, we're gonna discuss a type of Paris cyclic reaction called a Sigma Tropic Shift. So what is a Sigma Tropic shift? Well, it's an intra molecular Perry cyclic reaction in which zero pi bonds are destroyed after a cyclic mechanism. So we know this by definition, remember that Sigma Tropic shifts where the type of Paris cyclic reactions that occur with no pi bonds being changed between the reacted in the product. And that's exactly we're going to see in this example. I will get to this example in just a second, but let me give you a few more tips about what a Sigma Tropic shift is. So the pi bonds aren't gonna change. But what it does involve every single time is the breaking of one Sigma bond. So a signal bond is gonna break, and then the making of a signal signal bonds. So what we're basically doing is that the double bonds aren't changing. In fact, they do change position, but they're not changing in terms of quantity. The Sigma bonds aren't changing in quantity either, but it's important to note that that's actually ah, very big change that happens here, which is that one Sigma bond is destroyed and another signal bond is created. So what that means is that these reactions are usually going to take the form of numerous types of rearrangements. Usually you're not gonna see Ah very distinct difference between the product and the reactant where they look very different from each other. It's usually just that something is going to rearrange or shift. And you're going to say, huh, I wonder what happened. And afterwards, by looking at counting the number of pi bonds, you can tell this must have been a Sigma Tropic shift. Okay, Um, because of that, the products are typically constitutional ice summers of the reactant. So what that means is again, nothing's changing. No atoms are changing, but the way that they're connected to each other is changing because you're making bonds in your baking bonds. So usually there's gonna be constitutional items of each other. Very common examples of these, which you may or may not have to know based on your class and your professor. But some very, very common examples are the co pre arrangement, and the place and rearrangements will go on to learn these in depth. If It's something that your professor and your textbook requires. But I'm just letting you know that even if you don't need to know them, these are examples of Sigma Tropic shifts. Okay, cool. So let's look at this. Um, let's look at this reaction and try to figure out the mechanism. So once again, we have. This is a heat activated reaction where I'm basically starting off with to buy bonds, and I'm ending up with again two pi bonds. So we know this is a Sigma Tropic shift because this is a constitutional isom er of the first one, but nope, I Bonds changed. Okay, Now let's try to figure out what would be a mechanism that would make sense here. How could we create something like this, right? And guys, it's once again, it's gonna be cyclic. So we're going to see is that you're breaking upon and you're making upon. So in this case, which is the bond that we're breaking, we're breaking the one that was right here. OK, so it's actually where we want to start our arrows from note that you have to, because it's concerted so you can start from anywhere but just to think about it logically. It makes sense that you would take these electrons and make a double one here. Then you would take this pipe on and make a new sigma bon here. And then if you make that bond, you to break this pawn and put the dog on there. So once again, we have this Perisic concerted reaction. But it's leading to just the formation of a constitutional ice for Okay, So in the next video, we're gonna talk about how do you name and identify Sigma Tropic ships?

All right. So there are numerous types of Sigma Tropic shifts out there. Some of them have common names like the cope shift, the cope rearrangement or the place and rearrangement. But we don't. The most important thing about naming Sigma Tropic Shift isn't memorizing specific names. It's how to identify the actual nomenclature of the reaction. So that's what I'm gonna teach you right now. Thankfully, there's a shared nomenclature amongst all Sigma Tropic shifts, and that's what we're gonna learn. Now I'm going to teach you how to apply this nomenclature to the example that we just saw above. So the Sigma Tropic Shift is always referred to as an ex comma y Sigma Tropic shift, where X and y are different numbers of Adam's. Okay, so what does this mean? Well, the first Sigma bond that's broken So remember that you are always breaking upon and you're making upon right. So the first one that's broken is going to be considered Adam one. So the the atom that is that bond is being broken on is going to receive the title of one Now, this is not This has nothing to do with AIPAC nomenclature. So this is not us trying to name the compound from scratch. This is us. Just trying to name the reaction that's happening, Adam. One would be where the position where a break has happened or the destruction of a bond has happened. So then what's the X y? That has to do with where the new signal bond is created. The position that the new Sigma Bond is created would be the X and the y. Okay, so basically, what you would do is you would say that you are taking the electrons from one Adam, and you're putting them in between these other two atoms. And those other two atoms are gonna be your X and y. Okay, so let's go ahead and look at an example up here where we have once again our Sigma Tropic shift. So which one is the bond that was being broken? What do you see? What's what's the bomb that was being broken? It was this one. So that means that both of these atoms get labeled as one. Okay, Because in this case, I broke in the middle of a chain. I broke a bond right in the middle of chain. So Both of those received the number one. Okay. Now, does that mean that my numbers are one comma one? No, because for the x and Y part, we have to look at where was a bond made? So where was a bond made? Well, let's see. A new bond appears to have made Thio have been made here. So we have to do is you have to count from both chains. What? Adam's What's the number of Adam that it would take to get to that position? So for the top one, it would be two and then three for the bottom. It would be two and then three. So the bottom the bond that was broken was one. And the new bond was created in between Adam three and Adam three. So what that means is that this is going to be a three comma, three sigma Tropic shift. Cool. Awesome. So now we just did one example. And now what we're gonna do is we're gonna do four more examples of common types of shifts, try to do it first, and then I'm gonna tell you the right answer