Alright, so there are numerous types of sigmatropic shifts out there. Some of them have common names like the Cope shift, the Cope rearrangement, or the Claisen rearrangement. But the most important thing about naming sigmatropic shifts isn’t memorizing specific names, it’s how to identify the actual nomenclature of the reaction. So that’s what I’m going to teach you right now. Thankfully, there’s a shared nomenclature amongst all sigmatropic shifts and that’s what we’re going to learn now. And I'm going to teach you how to apply this nomenclature to the example that we just saw above. So the sigmatropic shift is always referred to as an x, y sigmatropic shift, where x and y are different numbers of atoms.

Okay. So what does this mean? Well, the first sigma bond that’s broken, so remember that you're always breaking a bond and you’re making a bond, right? The first bond that’s broken is going to be considered atom 1. So the atom that has a bond being broken on it is going to receive the title of 1. This has nothing to do with IUPAC nomenclatures; this is not us trying to name the compound from scratch. This is us just trying to name the reaction that’s happening. Atom 1 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 sigma bond is created. The position that the new sigma bond is created would be the x and the y.

So basically what you would do is you would say that you are taking the electrons from one atom and you’re putting them in between these other two atoms and those other two atoms are going to be your x and y. Okay? So let’s go ahead and look at an example up here where we have once again our sigmatropic shift. So which one is the bond that was being broken? What do you see? It was this one. So that means that both of these atoms get labeled as 1. Okay? Because in this case, I broke in the middle of a chain. I broke a bond right in the middle of the chain. So both of those receive the number 1. Okay? Now does that mean that my numbers are 1, 1? No, because for the x and y part, we have to look at where a bond was made. So where was a bond made? Well, let’s see. A new bond appears to have been made here. So what you have to do is you have to count from both chains, what atoms, what's the number of atoms that it would take to get to that position. So for the top one, it would be 2 and then 3, for the bottom it would be 2 and then 3. So the bond that was broken was 1 and the new bond was created between atom 3 and atom 3. So what that means is that this is going to be a 3,3 sigmatropic shift. Cool? Awesome. So now we just did one example and now what we’re going to do is we’re going to do 4 more examples of common types of shifts. Try to do it first, and then I’m going to tell you the right answer.