Now I want to go on to the next type of rearrangement. It's a little bit less common, but you're still going to see it and that's the 1,2-alkyl shift. The 1,2-alkyl shift occurs when only small alkyl groups are located on adjacent stable carbons. What that means is that you only do a 1,2-alkyl shift if no hydrogens are available. Why? Because it's a lot easier to move a hydrogen over than it is to move a methyl group or an ethyl group or some alkyl group over. So what you want to do is to do the hydrogen shift first no matter what. But in the case where there are no hydrogens, then you are allowed to do an alkyl shift. Just so you guys know, the two types of shifts that are common with this are the methyl shift and sometimes you will see professors use an ethyl shift. But I've never seen anything higher than that. The reason is that the bigger these alkyl groups get, the more energy it takes to move them over. By the time you get to propyl, the activation energy to make that happen is just overwhelming. It just doesn't happen anymore.

Okay. So here we've got another one. Let's go ahead and make our carbocation first. How do we make our carbocation? Kick out the alkyl halide. So what I'm going to get is a carbocation that looks like this. Are you guys cool with that? Cool. And then plus Bromine ion.Br^-

Alright, now I've got my carbocation. Is that able to shift to a more stable location? Well, let's say it went to the right. Would that make it more stable? No. It would just still be secondary. Right now it's secondary. How would it be if it went to the left? Yeah, that one on the left definitely has a lot more groups than the secondary. So now I have to ask which shift do I use? Well, do I have any hydrogens attached to that carbon? No, I don't. So that means my only choice is to do an alkyl shift. Now all three of these alkyl groups are the same size, so typically I'd want to pick the smallest one. But since they are all the same size, it doesn't matter which one I use. I'm just going to use the one closest to it, but I mean the one that I drew closest to it. But these are all even the same distance away; that's just the way I drew it; it happens to look closer. So now what would the arrow look like? The same exact thing, it would just come from the bond to the carbocation. What this means is that now I'm going to get what we would call a 1,2-Methyl shift.

And what I would wind up getting is now that I have an extra carbon coming off of that one down there and now I have a carbocation there. Why? Because the carbon here used to have four bounds, but now it only has three because the methyl group left. So now I just went from a secondary carbocation to a tertiary carbocation. And that's going to be a lot more stable. Does that make any sense? So remember, a hydrogen shift is the easier one, then alkyl shifts come next. Methyl is before ethyl. Ethyl is like your last resort. We rarely see ethyl shifts, but it is possible.