Leaving Group Conversions - Using HX

as you guys might have figured out by now. Alcohol, Zahra. Pretty important functional group for organic chemistry. But there's one major limitation of alcohols, and that's that they make terrible leaving groups. Okay, remember that the definition of a good leaving group is something that once it leaves its stable well, alcohol. After it leaves, it becomes O H minus. Oh, H minus is the same as ah hydroxide base, which is a very unstable molecules, a very strong base. So that means that whenever we have an alcohol were a little bit stuck. We don't know exactly what to do with it, because ah, lot of reactions in organic chemistry require leaving groups and alcohol isn't a good option. But wait, there is a solution. It turns out that a major topic that we're going to discuss in this section is how to turn alcohol into a good leaving group, All right. And it turns out that there's two major options like a fork in the road. We can take two major pathways and that they're both gonna lead toa awesome outcomes. They're both gonna lead to alcohol being a much ledbetter leaving group. Okay, so let's go ahead and talk about the first one. The first option that we have is to convert alcohol simply into an alcohol. Hey, lied. Okay, Now, remember that alcohol highlights have the molecular formula, our X, and the reason that they're such good leaving groups. Because Xnegative, once it takes off, is very stable. X could stand for iodine or bro. Mean or chlorine Thes air. Very Electra. Negative atoms that don't mind having a negative charge. So Al Kyohei lives are an awesome option. But another option that we also have that we'll discuss in a little bit is Sultanate Esther's. Okay, now, you might have learned already that Sultani Esther's make great leaving groups. I actually have talked about that before, but now we're gonna learn is how to actually turn an alcohol into a sulfa. Nay, Esther, so that it could become a great leaving group. Okay,

So let's start off with this page. I just want to do the alcohol slides, and later on, we'll talk about self any Esther's. So it turns out that the degree of your alcohol is going to determine which method you used to turn it into an alcohol. Hey, lied. Okay, um and that has to do with the mechanism. Okay. The re agent might be the same, actually, but the mechanism is gonna be slightly different. So for a secondary or tertiary alcohol. Okay, what's common to both of those is that they both make relatively good car will cat irons. Okay, If I were toe kick the o h off somehow and make it stable and kick it off completely, I would get a carbon Catalan. That's pretty stable. So it turns out that secondary and tertiary alcohols proceed with an S N one mechanism. Remember, that s and one is a two step mechanism that makes the car will carry on first. And then its nuclear physically attacked. All right, so let's go ahead and kind of figure out what's gonna happen. All right? So in the first step, what I'm gonna do is I'm gonna protein eight My alcohol with my strong acid H x. Okay. We're always gonna use H x a strong acid to turn alcohol into a good leaving group. Okay. And let's just say that the X stands for BR Okay, so I have HBR in my first step. What I'm going to get is alcohol grabbing a proton and kicking out the BR. What that's going to make is that's gonna make a water where the alcohol used to be. Now keep in mind that that water is now way better, like in terms of it's a much better leaving group. So what's gonna happen in the next step? We just protein ated happens in the next step is that just leaves completely on its own. Why? Because there's an s and one reaction. Remember that in an s and one reaction, you need to make a trouble. Cat ion. So we're gonna do now is we're just gonna draw out our carbo Catalan. And the reason that we knew that it would make a Carvel Catalan is because if you'll notice I started off with a tertiary alcohol, remember that I told you, tertiary is and secondaries are gonna do s and one. Okay, so one question you guys might have is Johnny. The metal group on the red structure used to be on the dash, and now you just drew it on a stick. Did you do it on purpose? Did you mess up? Well, actually, I did that on purpose. The reason is because remember, Carvell, Catalans are tribunal plainer, so you should draw everything on the same plane. It's actually not correct to keep it on the dash. You should just draw everything on the same plane. So now you might have guessed it. What's gonna happen to this positive charge? Well, keep in mind, that could rearrange if it was unstable, it could have rearranged. Would this Carl Cannon and want to rearrange. It's already tertiary. It's happy. So let's go ahead and attack it with the BR. Okay? And what? I'm gonna get it. The end is an alcohol. He lied. That looks like this. Okay, now, one note I purposely didn't include stereo chemistry here. The reason is because I don't know which side it's gonna attack. It can attack the front or the back. Okay, So, technically, you're going to get in anti MERS from this attack. Okay, You're gonna get a BR in the front and a br in the back. But typically, that doesn't really matter too much, because we're gonna be usually making this leave anyway later. Okay, so now you might also be wondering, Johnny, what was the point of this? Well, I'll tell you the point. The point is that alcohol wasn't gonna do anything. It was just going to sit there forever. So by reacting it with H X, what we were able to do is turn it into an alcohol. Hey, lied, which is much more convertible alcohol. Hey, lights are much more functional. They could do a lot more things, so I just made my alcohol more functional by turning it into an alcohol. Hey, lied. Now there is one more note that have to say, which is that the X in H X can equal two things. You can either equal iodine or it can equal broening. Okay, What about chlorine and flooring? Well, just so you know, flooring is too weak to react. Okay, so I'm just gonna put f doesn't happen. Okay, So it can't be f h f is not a strong enough acid to make this happen. Okay, but how will hcl will hcl The seal is still a pretty strong nuclear file, but it's not strong enough to make destruction happened in full yield in the high yield. So we usually do Is if we really wanna have a c l instead of the b r. We're going to couple that with a Lewis acid catalyst that is zinc and to Clarence together. Okay. And what that's gonna do is it's actually gonna make the leaving groups stronger. So let me just show you really quick how that works. By the way, this together, having hcl and the zinc and the zinc complex together is going to be called the Lucas re agents. Okay, some professors don't care that you know that some books don't really teach it, but in general it is kind of widely known as the Lucas re agent. Okay, really, it's going to do the same exact thing is what we just did accept. It just has one extra step. Okay, which is this? Basically what we do is we take our alcohol and I draw a little bit smaller, okay? And what's gonna happen is that the Lewis acid? Remember that a Lewis acid is a proton, Except, er I'm sorry. Wow, it's I'm sorry. Ah, Lewis Acid is an electron pair, except, er, it has an empty orbital. So what's gonna happen is that the Lewis acid is actually gonna couple toe to the oxygen. The oxygen is gonna donate electrons to the zinc. What that's gonna make is something it looks like this where I now have Oh, h I'm zinc with two chlorine and that oh, is gonna have a positive charge. Okay, what's great about that is that now, that is a much better leaving group than just water by itself. Remember that over here, I also had O. H. Two plus, but this one's even better. So what that means is that the c l. When it comes in, it's gonna have an easier time. Um, it's gonna have an easier time attacking their Okay. What's basically gonna happen is that it's gonna have an easier time leaving by itself. So once it leaves, okay, What I'm gonna wind up getting is a Carvel Catalan. That is than easier for my seal toe attack. All right, so that's the first situation I want to tell you guys about. Okay?

What about a primary alcohol? Well, if we have a primary alcohol, then the only thing that really changes is the mechanism. Primary alcohols are really good at having a backside on. They're really bad at doing making car will cat ions. So that means if I use h X once again, I'm gonna protein ate in my first step. Sort of gonna wind up getting is Oh, h h positive. Okay, But if this left by itself and then obviously I would get the X leaving by itself, so I'd get plus Xnegative. But the problem is that this can't just leave and make a stable car, Will Catalan. So, instead of we're gonna do is we're gonna do a straight up backside attack where the X hits the back side and kicks out the water. Okay. Now, the reason this is possible here, but it wasn't possible with the other situation is because the primary alcohol has a much better backside. It has a good backside since as a good backside, it's easy for my ex to just kick out the water all in one step. So we're going to get here is and alcohol. Hey, lied once again. But in this case, my mechanism was different. I used s and two instead of s and one. All right. Same exact thing would apply if I used HCL and the Lucas re agent what I would get wind up getting is oh, h within a zinc and to chlorine and a positive charge and what you would get in the second step is that my chlorine or not in the second step, but well, yeah, technically, in the second step, my chlorine would do a backside attack and kick out that entire complex. So then, in this case, if I was reacting specifically with those re agents, I would get a chlorine. All right, so really, this isn't that bad. I just went through the mechanism, so you guys will understand it, But really, all you need to know is HX. It's really that easy. You just take a checks and you can convert alcohol to an alcoholic. All right, Awesome. So let's go ahead and move on to the next topic.