Now we're going to talk about a way that we can make double bonds out of alcohols and this is through a mechanism called acid catalyzed dehydration. Okay, so how does this work? Well, remember back to when I talked about leaving groups in the past, Okay. And a leaving group is even a concept from acid base chemistry. All it means is that it's something that really doesn't want to leave something that really doesn't want to get a negative charge. So another word for leaving group is just conjugate base. Okay, so if you maybe don't really remember exactly what a leaving group is, just think conjugate base back to acids and bases. And basically, alcohols are really bad leaving groups or they're really bad conjugate base is they hate to become o h minus. Why? Because all which minus is actually a really strong base. Remember that you always want to go from stronger or weaker If we're making o h minus hydroxide, that's a really strong base. Okay, so this is not gonna be very favorite to just leave a molecule. But it turns out that there is one thing we can do to make alcohol a better leaving group, and that is to use acid. Okay. And if we can use some kind of acid, we can actually convert alcohol into an awesome leaving group. That awesome leaving group would just be that we add an age to it. We protein ate it so it turns into water. And water is an awesome leaving because it's neutral. It loves to leave, and it loves to just be by itself in solution. Okay, so here's the general, the general formula. I'm not gonna show you the mechanism just yet. That basically what we have is we have some kind of alcohol, and we have some kind of acid over water. Now, in this case, I just put the general h a I mean really any acid. But your common acids. We're gonna be sorry about that. Any of the strong acid. So h two s 04 is seen all the time. Any of the hydrogen? Hey, lied strong acids. Um, I've also seen phosphoric acid. This is not really a strong acid, but it's still strong enough to make the reaction go. These are all very frequently used acids for acid catalyzed dehydration. Okay. And we're basically doing is we're taking an alcohol. We're gonna be removing two Sigma bonds were gonna be removing the alcohol and a beta hydrogen. Okay, so this is my Alfa. This is my beta carbon alfa and beta relative to the to the alcohol. We're gonna be taking away two different, um, Sigma Bonds, and we're gonna making one pie bond instead. Now that general reaction of taking away to Sigma's and making one pie is an elimination. So this is actually gonna be an elimination reaction. Okay, Hope that's making sense so far. Now, there's another reaction that you may have already learned, or that you will learn soon. And that's actually the opposite. It's called acid catalyzed hydration. Acid catalyzed. Hydration is a reaction where we go from the double bond and we go back to the alcohol. Okay, this is actually what's called in addition reaction. Okay, because if you remember back to the general types of reactions, we talked about that When you take one bond and you make it into two, that's actually addition. When you take two bonds and you make it until one that's elimination. So hopefully that makes sense. So, basically um, the addition part is gonna be the hydration. The elimination part is the dehydration. Okay. How do you know which one it is? How do you know if it's gonna be a hydration or dehydration? You just look at what you're starting with. So in this case, since I have my alcohol, I know that I'm starting with an alcohol, and I'm going to try to eliminate it with an acid to become a double bond. However, if I was starting with a double bond and I used acid, then I could add water to it, and that would become ah, hydration. Okay, in this step in this video, we're just gonna learn about dehydration. But I'm just asking you to keep this in the back of your mind later on. For when you do practice problems with hydration that this is the way that we tell the two reactions apart. Okay, so let's just talk more in depth about dehydration. There's a few facts I want you to know. First of all, the more our groups on that alcohol, the easier it's going to be to dehydrate. This is just the fact that might come upon it. May be a conceptual part of your exam or professor might even ask you, give you four different alcohols. Which one is the easiest to dehydrate? Tertiary would be the easiest secondary primary, and then is the worst. And then Oh, sorry. Um, I don't know what I'm trying to draw here, but basically, that method can't even happen because if it's a method alcohol, then or methanol that can't even eliminate because it's only got one carbon. Okay, so basically, the easiest one is tertiary. The worst one is primary. That's the first thing. The second thing is that the specific elimination mechanism that we use is going to depend on how easily the molecules gonna form a carbo cat Ion. Okay. And the understanding Carvel Catalans is kind of essential to these two mechanisms. All that means is that if you guys remember back to the trend of carbon caddy and stability, that tertiary Carvel Catalans are the most stable and primary Carvel Catalans are the worst. Okay, and then obviously metal is even worse than that. But like I said, method doesn't even get counted because we can't use it. Okay, so it's really the same trend as the one about ease. Basically, we're saying is that the easier it is to make a Carvel cat and a positive charge on a tertiary carbon, the easier. I'm sorry. The not only the easier it's gonna be to make it, but also, it's gonna change the mechanism as well. Okay, So what I want you to know for this section is that secondary and tertiary make pretty good Carvel cat ions. Okay. And then primaries make pretty bad. Carvel Catalans. Okay, so let's say this thes two are good and that primary is bad, and then obviously metals out of here, okay?

So let's go ahead and start off with my primary mechanism. Okay, So what if I have a primary alcohol? We know it's not that easy to dehydrate. It doesn't make good carbo cat ions. So what mechanism? Where we're gonna use. Okay. And it turns out that for this mechanism, because we don't want to use a carbon cat ion, we're going to use the E two mechanism. Okay. And the E two mechanism, if you guys remember back to elimination is a concerted mechanism. Okay? That means everything happens at once. Okay, So where we going to start with this? Well, if you guys remember any time that we have an acid catalyzed reaction anytime it says acid catalyzed. Okay, this might be the first time that you've heard me say this, because maybe you haven't watched those videos or it's cool. That means that you're always going to get a pro nation step at the very beginning. Okay. Pro nation just means I'm adding a proton to something. So whenever you hear me say acid catalyzed even the supplies for or go to think Oh, there's gonna be a proton added to something. Okay, so in this case, I'm starting off with an acid notice that the asset I'm using here is age three h plus. Okay, now, that's actually a conversation in and of itself, because you're probably thinking, Hey, Johnny, what happened to the whole h A? Why isn't it like sulfuric acid? Well, because if you think about it, let's say I was using sulfuric acid. H two us, Oso four plus water. Okay, what's gonna happen is that any time you have any acid in water, that is always gonna be an equilibrium with the deep throat nated form. So what that means is that I'm going to get h 30 plus plus the the anti on. So that would be basically, um h s negative. Okay, Does that make sense? So basically, what I'm trying to show you is that no matter what acid you use, no matter if it could be a check, I it could be sulfuric acid. You're always gonna have h 30 plus as part of the solution, because you're going to get the water grabbing a proton from the strong acid and turning into a studio. Plus. All right, so here when I'm using h +30 plus, This is just gonna be our general acid that we use for these reactions. Okay, but if your professors asking you to draw the mechanism then obviously used the specific acid that he gave you, All right, so now we're gonna go ahead and start. The first step is pro nation. Do you see anything that's nuclear Filic or that has electrons that could grab this? Elektra Filic H. Okay, Now, keep in mind there's a strong die poll pulling away from the H that I have a partial positive here and a partial negative on the O. And the answer is that, yes, I have this oxygen with two lone pairs. It's very nuclear filic. It could go ahead and grab this age. Okay, but if it makes up onto the age, you have to break up onto the rest of the water, so we're gonna get it. The end of this first step is we're just gonna get ah, water molecule like that. Okay? And then plus, we would get plus another molecule of water, actually. OK, because we just removed a proton. Okay, so now here's the next step in the next step. I've got this water molecule noticed that I've got this down here and now I'm just drawing one of the ages That h was always there. I'm just gonna draw it right now, okay? And it turns out that in this next step, I'm going to do beta elimination now. Beta elimination members, just based off of your Alfa is wherever you're leaving group is in this case, alcohol was a terrible leaving group. But now I just protein ate it. So became a great leaving group. So I'm going to count this as my Alfa Carbon. My beta carbon is the one right next to it. Any carbon right next to Alfa is beta that has ah hydrogen on it. Can I eliminate? Yes. So I'm going to do a concerted three step mechanism where I do my nuclear fall to the H, Make it double bond kick out the leaving group, and what I'm going to get at the end is just a double bond. Plus check it out. An acid that originally had and now a molecule of water. Okay. The molecule of water came from the leaving group. The acid came from the nuclear fall That attack that h. Now what's important about the acid is that notice that the name of this reaction was acid catalyzed hydration. That means remember, the definition of a catalyst is that it's something that can neither be consumed nor destroyed in the reaction. All it does is it lowers the activation energy off the actual reaction. So it's really important that at the end of this reaction, you're ending up with the same acid that you started with. So if I started with H 30 plus, I have to make sure to get one molecule of H 30 plus at the end. Why? Well, because if you just didn't have HD plus present at the end, it wouldn't be a catalyst anymore. It would be something else. It would be a re agent, but since I'm regenerating it now, you know it's a catalyst. Alright, so I hope that makes sense. That was the E two mechanism that Onley applies. Just you guys know that only applies to primary alcohol, so if it's a primary, you would use this. But what about if it's a secondary or tertiary? Well, you're going to find out that's what our next topic is all about. So let's go ahead and see what happens when you have a secondary or tertiary alcohol.

The biggest difference between primary alcohols and secondary and tertiary alcohols is that secondary and tertiary. I told you guys can make more stable Carvel cat ions. So you already might be figuring that the mechanism is gonna include a Carvel cat iron for these structures. And that's actually right. So let's go ahead and get started. These mechanisms that addition mechanism that I'm gonna show you right now on Lee applies to secondary and tertiary alcohols. Okay? And these are gonna follow the E one dehydration mechanism, meaning that if you remember back to e one, e one is actually going to be a two step reaction. And it's gonna involve a carbon cada an intermediate. Okay, so let's go ahead and get started. In my first step, I'm starting off with an acid again. Notice that once again, I'm using h 30 plus, which is just my generic acid in water. Okay, that could have been any strong assets begin with. So now I've got alcohol. I've got my acid. Your first step of any acid catalyzed mechanism is to Protein e. So do you see anything that I could prote me easily? Yes, you do. There is an alcohol that has a very nuclear filic lone pairs. So I could take those lone pairs one of them and I can go ahead and use it to make a new bond to that very Electra Filic H or very acidic H. What that's going to do is it's now going to give me a leaving group that instead of being terrible, alcohol sucks. It's actually gonna be really awesome because it's just gonna be water. And remember that water is a good leaving group because it's neutral after it leaves. And what's better than to be neutral? That means it really wants to get out of there. Okay, now I've got my water. So here's the second step. The second step. I just said this was E one, by the way. Yeah, that was the first step is pro nation. But now we're actually onto the E one stage. So at this point, we need to do the first step because this is E one. Maybe you guys can predict what that first step would be. If you don't know. That's fine. Okay, if maybe you didn't watch that video or maybe haven't learned it yet, but It's just gonna be that the water leaves all by itself could so stable. It doesn't really need anything to kick it out. Okay. For the e two reaction, I needed to have a concerted three arrows. But in this case, I have such a great leaving group. It's just gonna take off by itself. And what I'm gonna wind up getting is a carbo cat eye on notice that in this case, that's a secondary carbo Katyn, which is pretty stable now that I have a car broke out. And there's one thing I should be watchful for. Do you remember anything tricky about Carvel cat ions? Okay, maybe you don't remember. And that's fine. But just you guys No carb. All Catalans like to do one thing. They like to shift. Okay. Okay. So carbo Catalans love to shifts, um, or stable positions. That means that at the end, they're actually gonna generate constitutional ice summers. So it's something really important to know in this case with this Carvel Catalan shift. No, because it's secondary. It doesn't matter, but and there's nowhere else that it can shift that we become more stable. But if I had a metal group around or something like that. This would be able to shift and become more stable. Carvel, Catalan. Okay, so now that we are mindful of that wants the last step. The last step is beta elimination, just like normal E one. So what can I do to eliminate it? I can use that conjugate base of my acid, which is just water. Pretty good nuclear file. It's OK, nuclear file. And I'm gonna go ahead and say that my carbon Catherine is the Alfa Carbon, meaning that any carbon that's attached to it would be beta. So this is Beta, and this is Beta. My question is, do any of these beta carbons have at least one hydrogen on them? And actually, they do They both have it. Least one hydrogen. Is there a difference between which one? I use? Could I use the top one or the bottom one and get the same thing? Yeah, it doesn't matter, because both of them would lead to the same product. So let's just go ahead and use the bottom one. So what that means is I would take my nuclear file, grab an H and make a double bond. So What that's gonna make is a new double bond. Okay, so this is the Pi Bon. This is my elimination product. Okay? Also, what we call dehydration product because dehydration is just the name for an elimination with water or with alcohol. And we would get the leaving group originally, which was water. Remember that water left in that first step and then we would also get h 30 plus. And what's the significance of h 30 plus that that is my catalyst once again. Okay, remember that we said it was important to get the same catalysts that you started with because that's the whole definition of a catalyst. Alright, So I hope that makes sense. Guys, it's pretty related to the other elimination reactions that we have toe learn in Oracle one. If you're struggling with these mechanisms, that means you have to go back or go forward, or whatever direction you need to go in your curriculum toe. Learn more about elimination. But hopefully this wasn't so bad. Okay, so let's go ahead and do some practice problems based on everything that we just learned

let's do some cumulative practice based on everything we've learned from acid catalyzed dehydration and make sure to be mindful of all the different details I taught you about which mechanism you would use and what would happen in terms of how many steps that would have and stuff like that. Now, there is one instruction that I want to give you. And that's remember that I told you that primaries would do in e to reaction or mechanism, and then secondary and tertiary would perform in E one. Okay, now, that is almost always true. But there is one exception of that. That is going to be if you have a primary alcohol that can rearrange toe a tertiary carbo cat ion through a shift, then it's actually going to do a carbon carrion mediated e one mechanism instead. Okay, so you're gonna have to use that information to maybe determine this first one. Notice that it is primary figure out. Okay, This would usually be e to if it could shift to a tertiary position, then you should actually use E one. But I'm gonna let you guys figure that out. 2nd, 2nd 1. Same thing you have to figure out what mechanism and everything that would happen in between. All right, So go ahead and get started on this first one, and then I'll show you guys how to do it.