Well, now what I want to show you is that just having a radical initiator present can completely change this reaction. The example I want to use is the same reaction, same reagents, a double bond with HBr. But now notice that there's peroxide present. Now remember that peroxide was a form of radical initiator. So what we want to do in this first step is instead of doing a carbocation mediated reaction, this is actually going to be a radical mediated reaction, which means that we're going to have to use the 3 steps of initiation, propagation, and termination to figure out what this is going to do. So let's go ahead and draw the first step which is initiation.

Now for this initiation step, this is going to be a little bit more complicated than usual just because I'm starting off with peroxides and this is actually not the radical that I want to use for my reaction. So my first step is going to be to generate my peroxide, so OR•2 equivalents of OR• radical. Okay? But then one of those OR radicals is going to react with HBr. So what that's going to do is that's going to make a radical that I can actually use in my reaction. That would be basically I would get, ROH, which is alcohol because I just got the OR attaching to the H and I would get Br• radical.

So I know that was a little bit longer than you used to for the initiation step, but you can consider that the initiation step isn't over until you get your target radical. Okay? In this case, now I have my Br• radical, which is my target radical. Now what I want to do is I want to react that with my double bond. Oops, I forgot to say propagation. Let's do it. Propagation. Okay? So for the propagation step, what we're going to see is we're going to have a double bond and we're going to have that radical. Now typically, in a regular radical reaction, I would expect this to react with one of the hydrogens on the alkane. But it turns out that double bonds are also very good sources of electrons. So instead of pulling off an H, it could just react to the double bond directly. So what I'm going to expect is that I'm going to get this electron moving into the space in between, one electron from my double bond also giving up, you know, also moving towards the Br to make a new bond. But now I have to figure out, okay, which atom does the Br attach to? Does it attach to the red carbon or does it add to the blue carbon? Both of these are attached to the double bond, so which one do I pick? And the answer is that we're going to pick the one that allows us to have the most stable intermediate. So basically, notice that this double bond had 2 electrons in it to begin with. Now, one of them just went out to meet the Br. Where is the other one going to go? And that's going to answer our question. It turns out that the last one would want to go to the place that's going to make it the most stable, which would be the tertiary location. If the radical is moving to the tertiary location like this, then what that means is that the Br must be attaching to the less substituted position.

So then what happens is that we have to generate original radical. This radical here winds up reacting with HBr. Okay? So then what I wind up getting is that, that, and that. And I finish off my product. And what my product looks like is now a bromine here plus Br• radical. Okay? I know my head was a little bit in the way for that, but you guys can hopefully see it. Okay? So that's our propagation phase. Notice that I did get an alkyl halide, but it's attached in a weird spot. And this is the part that's interesting.

This reaction, I haven't drawn the termination step yet, but let's just go ahead and fill in these blanks. What kind of intermediate are we dealing with here? We're dealing with a radical intermediate. So this is no longer carbocation. And because we're dealing with a radical intermediate, what that means is that this is going to be an anti Markovnikov addition of bromine. Okay? The reason it's anti Markovnikov is because notice that my bromine attached to the least substituted spot. So this reaction is very important because it's going to be one of only 2 reactions we learn in Organic Chemistry 1 that are anti Markovnikov. Okay? Just so you guys know, it's 2 reactions. 1 is called this. It's the radical addition of HBr and another one is hydroboration oxidation.

If you guys just remember those 2, you're going to be set because later on you're going to need to know that. Okay? But this is a big deal because now I know how to add halogens Markovnikov through a normal carbocation mechanism, but now I also know how to add halogens in an anti Markovnikov fashion and that would just be to add radicals. Okay? Let's go ahead and finish up this termination step. The termination step for this part, I'm not going to be picky. A lot of times professors don't really want us oh, I said terminal. Termination. Okay? Professors don't want to see all of the termination products for this. They just want to see you know what you're doing because there's a lot of radicals at the beginning. So all I would do is I would terminate Br• with Br•. Okay? That's definitely a possibility. And I mean, really honestly, the the 2 r groups coming together is going to happen even less than than before. So I wouldn't even put the 2 r groups together. That would be one termination and that would really be the main termination. Okay?

So basically, what we're going to be doing I mean, another termination would just be Yeah. Another very important termination. I'm sorry. Would be this radical. Okay. Just like reacting with a h radical or whatever. That would be another one. Okay. These are the ones that are favored. But other than that, the other ones really aren't favored very often. So you wouldn't have to draw all the different possibilities. Okay? So I hope that this makes sense, guys. You should be able to know how to draw the mechanism, but even more than that, you should be able to recognize when a reaction is going to be anti Markovnikov because it's using radicals. And this only happens when we're doing an addition of HBr using radicals. Okay? Cool. So I hope that made sense. Let's move on.