Ethers are generally unreactive. However, epoxides (3-membered cyclic ethers) are highly strained, so they are able to react with nucleophiles in ways a typical ether could not. Let’s take a look.
Acid-Catalyzed Epoxide Ring-Opening
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Now that we have a pox sides and know how to make them, it's important to know what can we do with them? And it turns out that ethers are highly un reactive. Ethers barely react with anything. But because the fact that Ip oxides are three member ID rings, they're very, very highly strained. So what that means is that even though ethers as a functional group are not very reactive, it Poch sides are because they have so much potential energy locked up in those bonds, they're gonna want to break open first chance that they get. So it turns out that we have two different ways that we can open the a pox, I'd ring, and they have to do with different agents that we use. So these air called the acid catalyzed bring opening reaction and the base catalyzed ring opening reaction. Let's start off with acid, and then we'll work on to base. Okay, so, in an acid catalyzed reaction notice, first of all, that I'm using the words acid catalyzed. Okay, that actually already gives us a hint about the mechanism. Okay, remember what I said Whenever you have an acid catalyzed mechanism, what's the first step Gonna be pro nation. You always need to protein eight first. Okay, It says that's a catalyzed. Always need to protein eight first. So what that means is that the very first step is that if I'm using an acid within a pox side, the oh, the nuclear Filic Oh, is going to go ahead and grab the h from the acid, because that h has a positive charge. So now what I'm gonna get is a molecule that looks like this where everything is still in the same exact place. Okay, except that I've got a formal charge on this positive on this. Oh, okay. Because the O has too many bonds. Alright, so now what happens? I've got a c l minus and the c l minus wants to break open the ring, but is trying to decide which side is it gonna break? Is it going to break the most, substituted the tertiary or the least substituted the secondary? Okay, that's supposed to be a three, by the way. Let me draw it again. The tertiary or the secondary. And the answer to this is that the chlorine or whatever and I and we're using, even if it was just a neutral nuclear file, is going to be the most attracted to the side of the ring with the most positive character. Okay, so we're looking at is the side of the ring that could stabilize that car broke a tie in the best. Because that I mean, I'm sorry. I just said Carvel cat And it's not a car mechanic. It's just a Catalan. It's just a positive charge. But that positive charge can d localize a little bit into those two different atoms. So the question is, which side is gonna be the one that has the most positive character, the secondary or the tertiary? The answer is the tertiary. So I'm gonna go ahead and attack here, And if I make that bond, I have to break a bond. So I'm gonna break the bond to the oh, What this is going to give me is a new compound that looks like this. Let's say that this bond right here is the red bond that I'm drawing here. Okay. Oops. That red is the same. Is this? What is it gonna have on it? Well, let's say that this chlorine attached from the front right there. What else would have what would have to metal groups? So I'm gonna draw metal metal, okay. And then on the other side of the red Bond, what I'm gonna have. Well, if the chlorine attached from the back, what that means is that the alcohol is going to go. I mean, from the front, the alcohol is going to go to the back. Okay, By the way, this alcohol I'm drawing here is just that right there. Notice that it's still attached in this position. Okay, so it's still gonna be attached. They're all right. On top of that, I'm still gonna have to. Other groups are gonna have a pro poll, and I'm gonna have a h so that h would just stay where it is in the front. Okay. Obviously, you don't need to draw. H is. So at the end of the day, I could have just drawn this without age. Okay, I could just erase that if I wanted Thio. Okay. Does that make sense? So notice what? My product is here. What my product is that I'm gonna get my product is is that I'm gonna get a nuclear file attaching to the Mawr substituted position. Okay. And I'm gonna get alcohol at the least substituted position. Okay? Just so you guys know this is unique. Toe acid catalyzed ring, opening face catalyzed ring opening is actually gonna be different, okay?
Acid-catalyzed ring openings favor addition to the MOST substituted carbon (thermodynamic control)
Opening of 3-membered intermediates/molecules always results in anti-addition.
Base-Catalyzed Epoxide Ring-Opening
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So let's go ahead and check out Base catalyzed. Now, let me know if you have any questions. Will acid? Let's go into base. Okay, so in a base catalyzed ring opening, what I have is that I'm starting off with a nuclear file right away. And there's no prote nation step because obviously don't have an acid. Okay, so what that means is that all I have is an O. H. Negative for some kind of nuclear file, looking for a way that it could break open this ring. Okay, because the ring is highly strained. Well, this always negative. Since there's no positive charge, it's not gonna be attracted to the side that's more substituted. It's actually gonna be attracted to the side. That's the easiest toe access. So for this one, I'm actually going to go ahead and look for the least substituted position, and that's the one that's gonna be favored because that's the easiest one to form. So in this case, if my choice is between secondary and tertiary, I'm actually gonna go for secondary. So I'm gonna go ahead and attack that carbon, which means I'm gonna break that bond and what that's going to give me is a new molecule that looks like this. Where? Let's say this is my red bond again. And this is the red bond here. What I would have is let's see it. The O h attached from the front. Let's say that my nuclear file attached from the front that means that Yep, I would get my propel group, and I would get my hydrogen, which I don't have to draw on the other side, which I would now get is an oh, minus on the backside. Okay. Now notice that once again, these products are gonna be anti to each other, because every time you break open a three member ring, they're gonna be anti because they're gonna snap out of place, and they're they're gonna just goes far from each other as possible, Okay? And then I have to Metal group. So I'm just gonna write that there to metals. Okay, so that's the end of that step. Now, typically, we're gonna assume that the own negative will protein eight. Okay. So typically, there will be a pro nation steps. Sometimes your professor will add, like, over water or something like that. And if there was water. Or usually we just assume that the end product is protein ated. So if it was protein ated, what would it give us? Okay, what it would give us is actually gonna be what we call a dial. Okay? So check this out. Look what I'm gonna get the end. What I'm going to get is I'm gonna get an O h. Going towards the back and in ohh. Going towards the front. What's the relationship between these alcohol's? Well, first what? We call this a dial? Because there's two alcohol's that's easy. Just die. All there's two of them. There's actually a special type of molecule that will study more in depth. Okay, so we have a dialogue, but also the relationship would be visceral. Can't remember that. Visceral is the word that we used to say that they're next to each other. That's the same thing of saying 12 Okay, so these air visceral dial's. But on top of that, these are anti because they are. They're trans to each other. It means that it was an anti mechanism. So the entire idea behind this is that this is what we would call an anti visible di hydraulics elation. That just means we're adding to alcohol's. Okay, why is this important? Well, this isn't the only way. This isn't the only type of base catalyze ring opening you could do. In fact, we could have used any nuclear file. I could have used a nitrogen or another type of oxide or whatever, but this specific one where I used N a. O. H is very important because it's what really one of the only ways to make these anti visceral dial's. That means I have to. Alcohol's facing opposite directions next to each other. This is important because there's another reaction that you're supposed to know called sin Visceral Dial's and sin, visceral dial's or did hydraulics. Elation is a completely different mechanism, So these air gonna go hand in hand and you're supposed to recognize both of them. Okay, if you haven't learned sin versatile Dial's already. You will learn it soon because I'll teach it to you. Okay, but anyway, I just want you guys to know that it's supposed to be You're supposed to ableto compare these two reactions to each other, and you're supposed to be able to know when you use in a park side with any wage and when you do the sin dialing reaction. Alright. So I hope that these two mechanisms made sense. If I were to sum it up once again, it would be acid is attracted to the most substituted based catalyzed, attracted to the least substituted. You always get alcohol at the end regardless, and that's really all you need to know. And then you're always gonna get anti products because you're breaking open a three member Great. All right, so I hope that made sense. Guys, let's go ahead and move on.
Base-catalyzed ring openings favor addition to the LEAST substituted carbon (kinetic control).