Radical Selectivity

Hey everyone. So up to this point, we've learned that radical imagination prefers to occur at the most stable radical catomine intermediate in most cases, that's the tertiary position. But in this video we're gonna learn that not all halogen are created equally. And in fact some halogen at times choose a spot. That's not always the best spot. Now, in order to think of this in everyday terms, just imagine you've been invited to the greatest steakhouse in the world where it has all types of meat selections, Whatever you could think of. Now here, we're going to attach this idea of our steakhouse that the different types of meat entrees you select and we're going to say that these meat entrees represent different types of elimination reactions and the more excel thermic your elimination reaction then the more non selective it is basically halogen it's anywhere on your organic compound and therefore the more unhealthy it is. Again, playing along with this whole idea of food selection. Now, this video is just taking a look at qualitative radical selectivity. And we're gonna go in greater detail later on and try to connect the idea of exo thermic reactions and selectivity. Now, first of all, what exactly is radical selectivity? Well, selectivity is defined as the ability to only for radicals to only halogen eight the carbons with most stable radical intermediates. Again, we're gonna learn that not all allergens play by the rules when it comes to this idea. Alright. So here we have four individuals that have been invited to this awesome steakhouse, the greatest in the world. The first one is not really picky in terms of food, they'll eat whatever, they are not selective whatsoever and they choose a typical hot dog. Okay, we're going to say that this hot dog which represents highly exotic thermic reaction also represents chlorination. Here. For nation has an entropy value that is negative 32. So really negative, really negative delta H. So it's very non selective, very unhealthy because we know hot dogs are made up of who knows what tons of different parts of animals. And we're going to stay here that floor nation because it's not very selective because this diner doesn't really care what they're eating. It is not useful in terms of radical elimination. So when we say for a nation we have f. two and we have ultraviolet light. We're gonna say it's a no go. It's two episode Thermic too uncertain. We don't know what it's going to do. It's so negative. In fact that in some cases we can deem that as being an explosive reaction. So we want to stay clear away from foreign nation and let's move on to our second person. So here the second person um is not willing to eat whatever they're kind of stuck in their ways. They only want to select something that they've eaten before. So they're going to play it safe. They're going to choose meatloaf and other dishes that they're familiar with. If we try to connect this to chlorination, we're going to say that the overall entropy value of chlorination is -101. Now here it's still excellent because it's negative but it's not as negative as Floor Nation because it's XR thermic, it's still a spontaneous reaction, which is good. But the issue is it's still just a little bit too negative as a result of this coronation, we're going to say the only useful radical coronations are reactions with a single type of hydrogen, meaning that if I choose an organic compound that has different types of hydrogen, primary secondary tertiary coronation will give me a mixture of products. It's not very selective. It'll do a little bit of here. A little bit of they're just like our patrons at this restaurant, they're only gonna stick to the foods that they know and they've eaten quite a few things. Now we have our third person. This person really knows their different types of meat selections and they know exactly what they want, they want the most expensive, they want the highest quality cut in terms of this here, they want maybe wagyu beef or something, something. They see that as being the most expensive. So this we relate to domination, brahma nation has an entropy valley that's negative 26. So it's still eggs, a thermic not as quite as an exa thermic as four Nation coronation, but since it's XR thermic, it's still spontaneous, we're going to say here that rumination is the only useful method for selectively hijacking al canes because you can control what it will ruminate. So when it comes to rumination, if we have a mixture of tertiary secondary primary hydrogen rumination always goes for the most stable radical cat down intermediate that's presented. And in most cases tertiary is more stable than secondary which is more stable than primary. Right? So we can count on bro mean to ruminate what we wanted to do. So here we have b. r. two H. V. And depending on what we have it will remain in the place that we want. And then finally we have our fourth person. So we've come to the greatest steakhouse, greatest um meat selection in the world. But then our fourth person says I don't want any meat, I don't want to get involved in any of this. So here we're going to relate this to Iota Nation. ι Nation has an entropy value that is positive because its entropy is positive is an indo thermic reaction. Remember endo thermic reactions are non spontaneous and it would require our investment of energy for it to go, okay so you'd have to basically uh push this person to try anything but again they don't really want to do that. They don't want to get involved in any of this meat selection. Just like I owed a nation doesn't wanna get involved with any type of radical elimination. So here again it's not spontaneous. So it doesn't even want to get involved. Now finally we're going to say here kyra products are always um randomized. So here we're talking about systemic mixtures now, what exactly does that mean? Well if we think about it, this has to do with if our starting material belongs to a Cairo center or not. So let's say that we had this organic compound and here we have a math group. And then here we have our hydrogen. Here we have fo and here we have proposed and we did rumination. Okay so brahma nation will want to replace this hydrogen here. Now that bro mean and either come in from the front or the back of the molecules in order to replace that hydrogen. So because it has those two options, we have two possible products. one where the bro men would be dashed and one And one word be watched. And then we'll just switch positions with the metal And you will get 50% of this one and 50% of this one. So you create a systemic mixture. We have 50% of both of these products. So that's what we mean by pira products are always maximized. So again we're looking at this qualitatively we're trying to relate the whole type of selectivity associated with the halogen based on the preference of different patrons within the greatest steakhouse in the world. Right? So again we're gonna go in greater detail in terms of this from a qualitative and quantitative analysis Later on. For now, this is just helping us to relate how the different allergens react when it comes to radical elimination.

would this first one b synthetically useful. And the answer is no. Okay. And the reason is because I have more than one type of hydrogen present, so my chlorine is gonna wind up not making good choices. Okay, Now, keep in mind. I do have a secondary position, and I have a primary position. Okay, so one of these should be the favorite one that should be secondary. But remember, chlorine doesn't like toe play by the rules, So it's just gonna wind up reacting with both. So I could expect to get a product that looks like a chlorine on the primary. And I could also expect to get a product that has the chlorine on the secondary. Okay, so here, in this case, I get a mixture of products. That's not good, because now I'm gonna have to separate them. That sucks. This is not synthetically useful. I would rather use a chlorine of College nation. That's not going to give me two different products. Does that make sense? So far? Cool. So let's go ahead and move down to the next one

So was number two synthetically useful? Yes, it waas. Okay. The reason this was synthetically useful is because I've got two different types of carbons. I've got the carbons in the middle and the carbons on the outside. Okay. Now, even though I have two different types of carbon, the middle ones are like Quaternary. The blue ones are primary because they're all attached to just one carbon. Okay, but my question is, how many types of hydrogen is do we have? Because not about carbons. It's about hydrogen. We only have one type because the red carbons, even though they're different, they don't have any hydrogen on them, so they don't really count. So what that means is that my product is simply gonna be Take any of these metal groups, you pick whichever one you want and just stick a chlorine on it, okay? And that would be my product. This is a matter which method group you pick because it's all the same. Just you just have to rotate it to look like the same molecule. Okay, So what that means is that this is a synthetically useful reaction I could use, bro me. And if I wanted to. Brolin would give me the same thing. I would just have a Brahmin instead of chlorine. But chlorine works as well. So it turns out that this is one of those molecules that actually works well with chlorination. If I want to use it, Okay. Doesn't mean you have to use coronation. You could also use Bram in ation. You get the same thing, but I'm just saying it's an option now. Alright. Whereas for the first one, that wasn't really a good option at all. All right, cool. So let me know if that makes sense. Let's move on.

So now that we're dealing with rumination, our lives really just get a lot easier. Because now all I'm gonna do is I'm gonna look for the most stable position, and that's the one. I'm gonna brahman eight. And that's it. Okay, so I've got once again secondary here. I've got primary here. I'm wondering which of these should I add the Brahman to? Should it be to both? No, I'm only gonna get one product. I'm just going to get the product with the Brahmin attached to the secondary position because Brahman just makes those good choices. It's gonna pick the radical that's gonna save it the most energy. Okay, now you might be wondering, What about these other positions here that I didn't circle? Should I also put bro means there Well, this one's secondary just like the red one. So that's the same thing. And then this one is primary just like the black one. And you know what? The primary isn't gonna form. So because this was symmetrical, I actually didn't have toe include those at all. It was really just a pic of choice between primary and secondary. An epic secondary. Cool. Easy, right Now that you know the trends, it's really easy. Okay, next question

how many products would we yield with this one will be. And the answer was to okay, The reason it's too, because in this case, I have to tertiary positions. Okay, so this is an example where maybe this isn't such a great reaction, Okay, because now I'm gonna have toe wind up getting molecules that are very structurally similar. I'm gonna have to separate them. It's gonna suck. But there was no better option. Okay, Chlorine, it would've been way worse. So this is just the best that we could do. Could I use iodine? New? Because that wouldn't even be excel thermic. It wouldn't keep you a chain reaction. Okay, cool. So I hope that made sense. Guys notice that these problems come a lot easier once you're not drawing the full mechanism, which you don't have to for every question, as long as you know how to do it in general. Okay, Cool. So let's go ahead and move on.

Now that you guys know the funny way to memorize which Hodgins they're gonna be more selective and which ones are less selective. Now, I want to teach you just really quickly the rigorous actual reason why Bro Ming is so much more selective than chlorination. And it doesn't really, technically have to do with how extra thermic it is. In fact, it has to do with the Hammond postural it. Okay, so remember what we learned about Hammond postulate. It is a way that describes what transition states look like. And the Hammond postulate is really the reason why Brahman ation is so much more selective than chlorination is. Let me show you guys that now. Okay? So once again, my definition of selectivity hasn't changed. But it turns out that I'm going to use the Hammond pasta to explain why pro nation is so much more selective. So, first of all, I just want to show you the reaction diagram for the energy diagrams for radical chlorination. Let's go ahead and look at the X axis first and just look at the coordinates. Notice that all of these things should look familiar. Basically, this is the first step of my propagation phase. Okay, so this is all propagation here. I'm just gonna put prop. Okay, so I got my propagation phase. We would expect that that takes energy because you're breaking a bond. Right? So that's gonna be this basically this activation energy here. Okay, that's gonna be the activation energy required to do that first step. Okay, then what that's gonna make is an intermediate that looks like that. Okay, that's a radical. That's my intermediate. And notice that here I put rate determining step. Remember that you're slow step. The one that makes the intermediate is always gonna be your rate determining step. Does that make sense? So far? Cool. So then what happens is that in the next part of my reaction diagram, there's, like, a story. Then what happens? Well, remember, propagation phase isn't done yet. I need to react my well in this case, this would be a termination step here. So let me just say here this will be termination, okay? And in my termination step, what I get is now to radicals colliding to make a new single bond. Now, just you guys know technically, this might come up conceptually. The activation energy for two radicals to collide and make a new bond is always gonna be exactly zero. This is just This is just a definition that you guys should know that the activation energy of two radicals colliding is always zero. It doesn't take energy for that to happen. So that's why there is actually no hump here. Okay, Usually would we would expect to see two humps, but there's no hump there because it doesn't take any energy for that to happen. Okay, Now, notice here that my overall entropy at the end of negative one on one, like I told you guys. But what's really important that I want you guys to know is what the transition state looks like. Okay, now, I'm not gonna go through this just yet. I'm just gonna let you guys know, pay attention to what that transition state looks like. Hammond's postulate, And now we're gonna look a rumination and see how Brahman ation is different

So for Roman ation. Notice that my energy diagram is a little bit different. I get the same first step. Okay, Same first step. And what I notice is that I get my same intermediate. Okay, Now, there's just one major difference between my intermediate here in my intermediate up their notice that the energy level for my rate determining step here is actually going to be endo thermic. Okay, What that means is that I actually having to put in energy in order to become this radical. Okay, Now look at the energy difference for my coronation for chlorination. It actually was extra thermic. It actually released energy to make that radical. Okay, isn't that crazy? So for chlorination, it was extra thermic to make that radical for Brahma Nation. It was Endo thermic. Well, what's the What's the significance there? What the significance is, is that remember that. What did Hammond postural it say? It said that basically Hammond postulates said that your intermediate is going toe look most like the side of your reaction or the the side of Yeah, the side of the reaction that has the highest energy level. Okay, so in this case, what that means is that the transition state for chlorination and rumination is gonna look radically different for chlorination. The thing with the highest energy, I'm just going to use Green as the highest energy is gonna be the starting molecule. Okay, so what that means is that my transition state looks a lot like my starting molecule. Notice that my my bond between the H and the stage two is really short. That means that the the intermediate looks a lot like the original Al Cane. Okay, Does that make sense? So far, So my intermediate really looks like the original. Now we notice is that for radical Brahman ation, my highest energy state is actually the radical. So what that means is that my intermediate looks a lot more like the radical than, like, the Al Cane Notice that in this case, my h is really, really far away. Meaning that this ch two almost already has a radical on it. Okay, Is that making sense? So far, So really, the biggest difference is the way that the intermediate looks. Okay, So why is that important? Well, because if you think about it, if the Al cane, if the transition state looks a lot like an owl cane. Then the energy savings of making an of of making a more stable intermediate isn't gonna matter that much. Notice that I have here, that this is the primary. This is this energy savings that I get as a primary radical. But if you make a secondary radical or tertiary radical, you save even more energy. Right? So you would think. Okay, it really wants to be tertiary so that it can make it dip all the way down here and be more stable. But no, chlorine doesn't care. Why. Because chlorine doesn't really look like the radical once it's in his transition state. Really? It looks like it's out cane. And the Al Kane was always stable to begin with. So it doesn't really matter whether it's primary, secondary or tertiary, because it looks like the out cane anyway, so it doesn't really need to have a stable intermediate. Okay, now let's look at Brahman ation for Bram in ation. What we notice is that it actually looks a lot like the radical already in the transition state. Okay, so if I can make it secondary, or if I could make it tertiary even better. That's going to make my transition state a lot easier to make. It's gonna make my transition stay a lot more stable, so the rate determining step can happen faster. Okay, so basically, that's the whole point. Rumination cares a whole lot more about making the graph look like this. Okay, because the intermediate, according Hammond's postulate, looks a lot like the radical. Okay, so what's this difference? Well, the difference is that remember that if you had a transition state that looked like the original starting product, you call that an early transition state, Okay. And notice that over here, what we wind up getting is a late transition state, because late means that it looks more like the second step. Okay, when you have a late transition state, you're going to care a lot more about how stable that transition state is, or how stable at intermediate is because it's gonna stabilize your transition state as well. Okay, so what I'm trying to say is that my simplification of the exo thermic rule works okay. But technically, the way that we explain selectivity is through Hammond's postulate. Okay, Now, for some of you guys, This is just gonna be theoretically. Just helps you know more about this class. Some professor is gonna be really picky about it and actually want you to be ableto describe this. Okay, so it's really up to you guys if you didn't totally get this. It's not the end of the world. It's probably not gonna be in your test. Okay? But I just wanted you guys to know it because I like to be thrown and like you guys to know everything. Okay, So let me know if you have questions, but if not, let's go ahead and move on.