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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.

10. Addition Reactions

Alkyne Oxidative Cleavage

In general, triple bonds are easier to cleave than double bonds. This means that we can use a variety of oxidizing agents to achieve cleavage, including potassium permanganate (heat is not required) or ozone. 

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concept

General features of alkyne cleavage.

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triple bonds can be cleaved in much the same way that double bonds were. And it turns out that we're gonna use really the same exact re agents for these kinds of reactions. Okay, so what I want to talk about here is the way that triple bonds react to strong oxidizing agents that wind up breaking those triple bonds. And we're going to call this cleavage of al kinds. Okay, So when you have a cleavage oven, al kind, what that means is that you're basically taking that al kind and you're splitting it into I'm gonna use the analogy of scissors. So you're taking these scissors and you're just cutting it right down the middle of that of that trouble, Bond. Okay, The way that we tell what the two products are gonna look like because it's gonna split the one thing into two is that we look at how maney carbons on each side. In this case, for this specific triple bond, I would have three carbons on one side, one carbon on the other. So I can expect that my two products are going to be the same thing where I get a three carbon chain on one side and a one carbon single carbon on the other loan carbon. Now it turns out that triple ones are very sensitive to oxidation. So what that means is that any strong oxidizing agent will work. Both Canada, four and ozone are gonna really produce the same exact reaction. And what I'm gonna wind up getting is a mixture of car box like acids for anything that's above one carbon and carbon dioxide for anything that's a single carbon. So in this case is you can see I had three carbons on one side. So that means I get a carbon carbon selic acid on that one side for the other one. I chopped off just a single loan carbon. So that one's gonna be fully oxidized to co two carbon dioxide carbon dioxide gas. Okay, that Onley happens when you're chopping off one carbon chains. Okay, so what I wanna do it's really easy. Just want to show you guys that So you guys know what I wanna do is this multi step synthesis practice and I want you guys to try it for yourself. So go ahead and look at this double bond. Look at these three re agents and try to figure out what the end product would look like. Based on what? You know what? These re agents, Okay. And then I'm gonna go ahead and give you the answer, so go for it.
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example

Predict the product of the following reaction.

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so I'm starting off with a double bond and I am halogen eating it. Okay, Since I'm halogen eating it, that means I can expect to get visceral die. Hey, lights along that double bond. So what I would expect for the first step is that I would get halogen that look like this cl here, seal here. Remember that they have to face opposite directions because it's actually anti the position of that. So that's a reaction that you should have known from the addition chapter. Okay, then we have, um NH and we're using it in excess now. That just means h minus in excess. Do you know what that would do to visceral Daylight's? Actually, What would it do to any detail? It's whether they're Gemina Orvis inal. It's gonna wind up doing a double elimination. So it winds up happening is that one of the h is from here, Eliminates with one chlorine in age from here. Eliminates with the other. So what I wind up getting is a triple bond formed so I would wind up getting something. Looks like this. Okay. Where I know it looks way different, but if you count my carbons I started off with five. 12345 I'm ending up still with five. Okay, It just looks a little funny. And the reason it looks funny, Because, remember, triple bonds have to be in that linear confirmation or that linear geometry. Okay, so now I've got a triple bond, and now I can finally Well, ah. Question you might be asking is Johnny wouldn't excess h minus. Take this all the way toe Alcon ID. So it has a negative charge. Remember that? Sometimes it had excess base. It could take it all the way to a negative. In this case. No, this could never be an Alka. Nine. Why? Because this is an internal alkaline. Do you remember the other type of al kind that we've talked about? We talked terminal all kinds terminal. All kinds can turn into alcohol because they have an H that could be deep rotated. This al kind here doesn't have any hydrogen directly on the triple bond. It's got an ethyl on one side. Ah, method on the other side that can't be deep rotated. So just gonna stay as a triple bond. I hope that makes sense. So now we're doing ozone. And this is gonna be an O's analysis reaction. That means I can expect to get carve oxalic acids and maybe carbon dioxide. So I have to go ahead and split this bond. We don't need to know the mechanism. I'm just gonna split that on into. And what are we gonna get? We're gonna get a two carbon section on one side and a three carbon section on the other. Does that make sense? So now that I know what my segments look like, I have to draw the car. Looks like acid. So I would get Ah, car. Looks like acid. That looks like this. Okay. Plus, I would get a car. Looks like acid. That looks like this. Okay, notice that one of these is two carbons. 12 and one of these is three carbons. 123 So, overall, it's adding up to five, which is what I needed it to add up to from my original. Now you might be wondering, Johnny, why didn't we get carbon dioxide like we got in this example here where I had carbon dioxide? Because carbon dioxide Onley forms when you have a one carbon segment, and in this case, I didn't. So this would actually be the final answer would just be too different. Carve oxalic acids. Alright. So I hope that was good practice for you. A multi step synthesis, but also just learning how to do oxidative cleavage off a triple bond. All right, so let's go ahead and wrap this topic up.
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