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Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

12. Alcohols, Ethers, Epoxides and Thiols

Ether Cleavage

Ethers are almost completely unreactive to reactions. They can only undergo one useful reaction – they can break apart in the presence of strong acid. 


How to predict the products of Ether Cleavage.

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Now I want to talk about all the different reactions that ethers undergo. And it turns out that you guys are in luck because there's only one. Okay, ethers air, actually extremely un reactive. They're very stable. So what that means is that there's almost nothing you have to know about ethers in terms of their reactivity, they're pretty much almost this un reactive. Is Al Keynes okay? But there is one reaction that they could be forced to do in the presence of a very strong acid. And that is cleavage of ethers. Okay, So, like I said, I was just trying to scare you guys. It's actually not that bad. Just one reaction. That's it. So ethers air Very combustible, like al Canes. They have a lot of energy stored in those bonds. But in terms of breaking those bonds hetero politically so that you get like a negative and a positive, that's very difficult to do with ethers because they're very strong bonds. So what were The only thing we can do is that we can cleave them in the presence of strong acid and the assets few super strong. It can only be h i or hbr. So what that means is HCL h f are not strong enough to make an ether Cleef. All right, so let me go ahead and show you guys this mechanism. Let's go ahead and work with H I since it's the strongest one. And basically what happens here? Is that the ether protein? It's okay. So what I wind up getting is that my oxygen and my carbon? That's a very strong bond. But what I can do is I can protein ate it first. Okay, What that's gonna wind up giving me is an ether with a formal charge. Okay, now that I have that formal charge and now that I have such a good nuclear file present member I negatives and very strong nuclear file, I could do a backside attack. So now what I can do is I can take this. I and I can attack the carbon chain, and I can kick out the O. H as a leaving group. Okay, What that's going to give me? Is it going to give me one equivalent of an alcohol iodide? So I'm gonna wind up getting ethyl iodide, and then I'm also going to get ethanol okay? Because I wind up getting the o h turns neutral again. So I wind up getting this plus this Cool. Right? But it doesn't end there, because now that I have the alcohol iodide that's done, the alcohol highlight is done reacting. But the alcohol can actually react again. Because what I can do now is I could take my alcohol, and I can protein ate it with another equivalent of h I. So what I'm gonna do is this and that. And what that's going to give me is that's going to give me Oh, h h positive. Okay. And then I haven't I Negative now, guys, if you have already studied the conversion of alcohols, too good leaving groups. Okay, then this is actually that same exact reaction. All we're doing is we're converting alcohol toe a good leaving group using h i. And that mechanism should be What do you guys know? Since it's a primary alcohol, it should be an s and two mechanism. Okay, So I would do a backside attack once again, and what I'm gonna wind up getting at the very end isn't gonna get another equivalent of alcohol iodide plus water Okay, So what this is going to create at the end is not one but two equivalents of the same alcohol. Hey, lied. So the answer for this question is that what I should put is two times that that is my actual answer. Because I'm splitting up the ether into due to different sections. I'm cleaving it, and I'm getting actual highlights as a result. Okay, I hope that made sense. So now what I want us to do is predict the whole mechanism for this cyclic ether. Um, now, this is a cyclic either, but it's not technically in a pox side, because remember, a pox sides or three member bring this is a five member drinks. So we would just call this a cyclic either. Okay? And I want you guys to use HPR to figure out what the end product is gonna be. Um, this is gonna wreck twice, just like the other reaction. So try your hardest to get this and then I'll show you guys the way. Go for it.

Predict the product of the following reaction.

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All right, so let's start off with the first step, HBR. We know that the alcohol I'm sorry that the O is gonna protein eight. So what I'm gonna wind up getting is a protein ated either with a formal charge, okay? And I also get this awesome nuclear file br minus. Okay, so the next step needs to be a backside attack. I'm going to go ahead and pick one of the sides. Doesn't matter which one to attack and kick out. The good leaving group, which is in this case, is gonna be a neutral alcohol. So what I'm gonna wind up getting now is some That looks kind of funny. It's gonna be It's gonna break open the ring, so I'm gonna get a bro meet up here, and then I'm gonna get the same ring as before, and then I'm gonna get oh, h okay. Just to make sure, let's make sure that there's the same number of carbons. 12341234 Sure, we drew it right. Okay. Now, keep in mind that we don't have to draw in this pattern where it's like, kind of like, looks like an old ring. We could just draw it as a straight chain, so it's actually convert that to a straight chain. What that would look like as a straight chain is just like I'm sorry. 1234 with a bro Ming on one side and with an alcohol on the other, Does that make sense? So I just kind of straightened it out. So now are we done? No, we're not done because we stop in alcohol present and we can convert that alcohol toe a good leaving group using another equivalent of HBR. So now we're gonna do is we're gonna do this, that we're gonna wind up getting the b are still intact. But now we get this good leaving group here water. And now we've got another br negative present. So that be our negative could do another s and too, And look what we get it the end at the end. We're gonna get a four carbon chain with bro means on both sides. So we wind up getting is what we call a terminal die. Hey, light from the reaction of ah cyclic ether with h b r h I we wind up getting a chain. That's the ring was broken with Halogen is on both sides. Terminal die. Hey, lied. And that's it. So one question you guys might be asking is Johnny does The professor is the professor just going to say HBR? Are they going to say HBR times too? Either way both mean the same thing. Okay, as long as you're Professor puts HBR there by itself, you're supposed to assume that that means in excess. Okay, so you're supposed to assume that there's enough HBR to convert the entire thing into a diet. Hey, light. Okay, now, the only exception to that which I really haven't seen, would be if your professor specifically says one equivalent of HBR. Now, if they said exactly one equivalent, then your end product would have actually been this because you wouldn't have that second equivalent possible. But in the absence of that information, if you just writes HBR, then you assume that it's an excess. Okay, Does that make sense? So then your answer should pretty much always be the terminal daylight or the diet highlight in general, unless you're Professor specifically states that you don't have that many equivalents alright, Cool. So I hope that makes sense. That's all you need to know about ethers ethers like they're much harder to make than they are to react with making them. There's a lot of different ways to make them, but in terms of reactivity, they really don't do anything. So I hope that wasn't too bad. Let's move on to the next topic.