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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
Dihydroxylation
In this reaction, we learn how to use certain agents to add diols to a double bond. This is also known as the 1,2-syn diols reaction.
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concept
General properties of syn vicinal dihydroxylation.
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So now we're moving on to yet another edition reaction. And this edition reaction is gonna be one that adds to alcohols to the same double bond and it's going to do it all in one step and this reaction is called Sin visceral di hydroxy elation. Okay, so how does this work? Basically? We have these two very special re agents, we have potassium permanganate and we have osmium tetroxide. This is common oh four and oso four that are both highly capable of adding oxygen's two double bonds. Now, it turns out that this mechanism you're not going to need to know the whole thing. Okay, But what you do need to know is you need to know what the end product is gonna look like. And as you can see it's really easy. All we have is a double bond. We add one of these two agents, It doesn't matter which one. Sometimes you're gonna see catalytic nm oh, that's just a catalyst that sometimes comes up. Sometimes it doesn't don't worry too much about it. And what you're going to get at the end is what we call dials, why? Because there's two alcohols in the same molecule, they have a visceral relationship. What's visceral mean? It just means that they're next to each other, they have a one to relationship and they are sin to each other or their cysts. And that means that the reaction was sin. Okay, so how does this actually work? Okay, the reason this works is because potassium permanganate and Austrian tetroxide. Both have a very, very similar structure where it's basically one central atom surrounded with as many oxygen's as possible now. The way that I like to think of this maybe just to make it really kind of fun is I kind of visualize that these look like spaceships. So this is like a flying saucer and there's a flying saucer and there's like a little like cockpit here with an alien inside. But of course he's got like four arms because aliens don't have the same amount of arms as we do and whatever. So we've got these we got these UFOs and what do they do? Well they fly down to Earth and they go attacking double bonds. Alright, so this Ufo is like coming, it's like swooping down on the double bond and it decides, hey, I'm gonna leave humans a gift, I'm gonna leave this double bond a gift. And what it's gonna do is it's just going to add an oxygen to both sides of the double bond, it's basically gonna take one of the oxygen's here, one of the oxygen's there and add them to both sides, leaving a dial at the end. Okay, please do not tell your professors that I just told you that. Okay, I sound like a retard telling you this mechanism where there's like a spaceship and it's like abducting like cows or whatever, like I don't know like I'm just making sh it up at this point, but I'm just trying to help you guys remember because I know there's been a lot of free agents today. Why the these agents are special and how you could think of what they do. Okay, so they're going to leave two alcohols behind and they're going to take off back into space. All right. Now, if you do want to know the mechanism really quick, I'm going to show you the first step. You don't need to know the whole thing, but it's going to look like this. Where if you have a double bond and you have um let's say we're using osmium tetroxide. So, double bond. Okay, what's gonna happen is you're gonna get a cycle ization reaction where my and there's a method there. I'm sorry. Where my double bond grabs one of the os. These electrons go down onto the osmium. Okay, And then these electrons go and make a bond to the double bond. Okay, So what winds up happening is that we get the cycle ization reaction. You wind up getting two alcohols at the end and then your os so far, I mean, obviously it's missing two oxygen's that thing just leaves and it goes back into space. All right. So, you might need to know the first step, but regardless, you're never gonna need to know the whole mechanism. All right. At least I've never seen that night in teaching or go for a very long time at a lot of universities. All right. So, let's go ahead and do a multi step reaction here. And what I want to do is just literally, you know, just have you guys go ahead and try to figure this out by yourself, and then I'll go ahead and jump in.
General Reaction:
You don’t need to know this entire mechanism, but I would suggest knowing the first step:
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example
Predict the product for the following multi-step reaction.
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Alright, guys. So what you'll notice is that I have a strong acid in water. Okay? So immediately, you should be thinking acid catalyzed reaction. But I'm starting off with an alcohol. If I'm starting off with an alcohol, that means that I'm gonna be going towards the AL Keen, Which means instead of being a hydration, this would be an acid catalyzed dehydration. Okay, Now, if you don't remember this mechanism, that's okay. I'm just gonna go through it again. That's fine. But this is in general, this is an elimination reaction. Okay? And again, if you don't, if you haven't learned these yet or maybe you're kind of week on them, that's okay. I'm just gonna show you the whole thing, all right? But the whole point is that I'm gonna get a double bond, and then I'm gonna be able to use Oso four to react with it. So how does this work? Basically, the first step of any acid catalyzed reaction is pro nation, so I'm gonna go ahead and protein eight. Okay. What this is now going to give me is it's going to give me an alcohol that looks like this. It's gonna give me a water leaving. Okay. Now, typically. Ah, primary. A primary water wouldn't be able to leave very well, because that's gonna make a Carvel cat. I am. Okay, but this one would be able to shift, so we are gonna make it leave. What's gonna wind up happening is that I'm going to get a car, Walcott, and it looks like this. Okay, now, this is a special type of Carvel Catalan because it's adjacent to a 34 or five member ID ring. Okay. And whenever you have, I'm gonna put your adjacent. So whenever you have a carbo cat and that's adjacent to a 345 million ring, what that means is that it's gonna be very strict. It's gonna have a lot of torch. It'll strain on a lot of angle strain. So instead of getting just a regular hydride shift or metal shift, we're actually going to see is a ring expansion. Okay, so we're going to get a ring expansion instead and bring expansions kind of vary from Professor professor. Some professors love ring expansions. They just give you every single time. Some professors don't really care for it so much so this is something that you just have to see in class if if they're using a whole lot of okay, but ring expansion what it does, is it? One of the carbons on the ring is literally just gonna engulf the other carbon. So what we're gonna do is we're gonna take that metal group, pull it into the ring and make it one carbon bigger. So now what I'm gonna do is I'm gonna get a Carvel cat, and it looks like this. Okay, now that I have my new carbo cat on its stable and I'm going to go ahead and do the elimination step, the elimination step is just gonna be with my br minus because I have to regenerate my acid and I'm looking for betas. So this is my Alfa Carbon. How many different beta hydrogen is? Do I have? Well, I only have one type because there's such a symmetrical molecule. So I would just take any of the ages and I would do my elimination step, which has grabbed the age, make it the whole bond. So what this is gonna make is a double on that Looks like this. Okay, so that was a good little refresher of acid catalyzed dehydration. If that maybe you haven't learned it yet. Don't worry. We're gonna learn more about this later. Okay? So now I've got this double bond and we're going to react this with Oso four. What is Oso four gonna do? To what? The whole bond, right? What Oso four is going to do is it's gonna make sin Dial's. So all I have to do I don't have to draw the mechanism. I'm just going to draw that. I'm gonna get to alcohol is coming off of the same bind. Do I have possibility for Indian tamers here? Do I have any Kyle centers? Actually, I do have Carl centers, both of these air Cairo. But this has a plane of symmetry. So this is actually a miso compound. So I wouldn't have to draw the other an answer because the other answer is the same thing. That's the whole definition of me so that it's not Cairo. So that's my end product here. Now, I did want to mention one more thing, which is just something that I might have forgotten to mention. Camera Four and Oso four both work. Really well to add Sendai ALS. But there's there's one exception for Canada for Onley when it's cold. Okay, if it's hot communal four, it's going to do something else entirely. Okay, but if it's cold, committal for it will add the sin. Dial's alright if it's hot. Don't worry, we haven't gotten there yet. It's gonna do something else completely different, okay?
Additional resources for Dihydroxylation
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