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Organic Chemistry

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19. Aldehydes and Ketones:Nucleophilic Addition

Wittig Reaction


Box-Out Method and Full-Mechanism

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Hey, guys, in this section, I'm gonna teach you possibly the most important reaction of this entire chapter. Are you listening yet? Good, because you need to. This is called the Wittig, or video reaction, and it's definitely gonna be on your test. So let's get going. All right, So the Wittig first, while you pronounce it also video because it's like German. So I say Wittig. But if someone says Vidic, don't freak out, okay, this reaction is a special way to make new carbon carbon bonds between Alba hiding key tones. And what it's gonna do is it's gonna make re geo specific Al Keane's. Now what do I mean by re Geo specific? Regio just talks about like locations, right? It just means that I can make a custom all keen with whatever our groups on it I want. That's actually pretty helpful because most directions that make all kinds have to do with elimination, and sometimes the our groups were kind of in different places. In this case, I can pick exactly where I want those are groups to be okay, so in general I'm gonna show you an easy way to do things. I'm also going to show you the whole mechanism. Of course. Okay, so the easy way to think of it is that you have a reaction of a carbon Neil and a molecule called in ill. It I'll define that Maurin a second. So when ill it when a carbon eel and an ill it come together? Um, obviously, it's kind of a weird mechanism, but the are groups wind attaching to each other through an Al cane. And I get my radio specific Al Keen as a product. Okay, so if you were to get a question on your exam about ah Wittig reaction and it's not asking for a mechanism, the answer this question be extremely easy because all you have to do is use the box out method. Okay, so this is something that I there's like a Johnny Special Clutch special. What's the box out method? Will The box out method says, Well, if a professor gives you a keystone Aldo hide plus an ill it all you do is you take them and you face them towards each other so that the phosphorus from the village and the oxygen from the carbon eel are almost touching. Okay, then what you do is you take your your little combination. There, you draw a box around the phosphorus and the oxygen. You start scratching out, you squint a little bit. Pretend like that's actually a big AL Keen in the back. And that's your answer. So, without a mechanism without any crazy memorization, look at that. We get our answer, which would be an age and an R in this case, on one side that came from the carbon eel and then whatever our groups you had on your ill it okay, so really straightforward. It's one of the funnest reactions to use because you just it's an easy reaction to toe learn. Okay, However, we know that organic chemistry two professors air so mechanistic they want you to know all the arrows. So, in case your professor is one of those, let's go through the entire mechanism. Okay, so the first part is the formation of the ill. It it turns out that the ill it actually comes from an alcohol. Hey, lied. Okay, that alcohol hey, lied is going to react with the molecule called a try. Federal Foss fiend. Try fennel. What? Three fanzines. Phosgene. Okay, now, guys. A try. Fennel. Phosgene has a very nuclear filic. Lone pair. Okay, so that nuclear feel like lone pair is actually gonna be able to do an s n two backside attack reaction. Okay, so you would take your alcohol. Hey, lied. And you would use that as you're leaving group, and you would kick out the halogen. Okay, so this is just an s and two mechanism from your or go one glory days, okay? And what you wind up getting is now the X is gone. The phosphorus is there. But now the phosphorus has a plus charge, right? Because, well, it's not too happy with four bonds. It wants three bonds in a lone pair like nitrogen. Okay, everyone cool. So far, we don't have until it yet, By the way, this is just to try funnel, fostering doing the s and to attack. Okay, Now, keep in mind, guys, everything you learned about s and two applies here, so it's not going toe going to work on what type of alcohol. Hey, light, You guys happen to remember this? Guys, if you're gonna learn anything in organic chemistry? No, your backside attack. Okay, you need You can never forget s into it. Even comes up in med school. Pharmacy school. What have you You're gonna need to know us and to you. Okay, You're shocked that I said that. But it's true. So it's not gonna work on tertiary alcohol. Hey, lights. Right, Because it's too blocked up. I can't access the backside, etcetera. Okay. Also think that it's gonna work. Fastest right? It's gonna work the worst on tertiary than a little better on secondary, much better on primary and then obviously the best on method. So if you were asked a question of which alcohol hey, lied would yield the fastest Wittig reaction. Well, you would go with one That doesn't s into reaction the fastest. Okay, so that's another type of question that you could see about which Wittig is the best. It would be the one with the least substituted occupy a light. But I digress. Let's move on to the next part. Okay, so now I've got my phosphorus with the positive charge, and I'm gonna deep protein ate it. Now, theoretically, I could use ah lot of different strong basis to do this, but for some reason, uh, There's a very popular base that's use specifically with this reaction that you don't see a lot in most of organic chemistry. And that is bully. What is bully guys? Bullies? Justin organo metallic. But it's a really strong base. Remember that Organo metallic or strong bases its beautiful lithium. So it literally looks like this. It's a four carbon chain with a negative charge analyst the, um, with a positive. Okay, remember that za super ionic bond? So you can just draw them as an ion and Catherine, if you want. Okay. Now, beautiful lithium. Extremely strong base is going to pull off. You're hydrogen, and it's going to deposit a lone pair onto the carbon. What this is going to do is it's gonna give me two charges that air next to each other on the same compound. I'm going to get a positive charge on my P. A negative charge on my carbon. This is what we call an ill id. Okay? Just, you know, and ill, it means that you have charges adjacent to each other. Got that? So far, charges adjacent to each other is an ill it. So I've got my positive and negative right next to each other. Now, depending on what type of question this is, there's two resident structures that you could use for this problem. Okay, First, let me just draw it. What would be the resident structure for this? Well, remember that phosphorus actually has a neck spanned ID octet, Right? So it can expand toe hold five bonds, which is unusual. We don't really deal with these that often, but you could use this negative charge to make a double bond. And this phosphorus is actually just fine like that, because now it has a double bond with three federal groups has valence of five. Because as five bonds one electron for each bond, phosphorus is happy in that arrangement. Okay, Now, these two different resident structures are good for two different things. This resident structure is the one, the first one. The Iliad is the one that I want to use for my mechanisms. Okay, so if you're asked to draw the full mechanism, this is the one you use. Okay? If you just have to determine the product. So if you're given an alcohol Hey, lied with beautiful lithium, etcetera. And it just has predict the product, then by far, definitely use this one because this one's gonna work for your box out, right? This one you could just put next to your carbon. He'll draw your box and you're done the ill It However, that's good for the whole mechanism. Okay, so now let's move on to the last step. The last step is Hey, I want to react this ill it with the carbon, Neil. So how does that work? Well, let's just take I got r one r. Let's just take on two. Beautiful. Okay, so I've got to beauty known, and I'm going to draw it like this to beauty known, and I've got this ill it next to it. So let me just draw that down here. P p h three Positive. Negative. Okay. What's gonna happen, guys? Well, what we're actually gonna form in this set situation is a nuclear filic edition. Okay? We're gonna form. There's a really interesting nuclear filic edition because I've got a negative charge and I've got an Electra Filic carbon. So this follows the same rules for nuclear look addition that we've been using this whole time. The negative would attack the positive kick up the Oh, I'm gonna get this crazy looking Tetra Hydro Intermediate, but it is a tetrahedron. Intermediate. Look at it. I'm gonna have um Oh, negative. Okay, Now, for the sake of drawing the next step, I'm gonna draw these are groups a little strange. I'm gonna draw that now. The beautiful is here. I'm sorry. Not the bugle. The ethyl is there and the metal is here. Is that cool with you guys? Because I need to draw everything connected. Okay, so I'm just kind of shifting it over. Then I'm gonna draw the new bond. This is the new bond that was created between the carbons. Now, this is the other carbon that's attached to a metal in a metal, right? And then I've got my p p h three positive. And guess what, guys? This is the ugliest Tetra Hydro intermediate in the world, but it still is a Tetra Hydro intermediate because this is nuclear Filic Edition, my friends. Okay, now, typically with nuclear feel like addition, what would happen is that I pro tinny and I'd be done with it. But this is the weird part because I've got the oxygen in the phosphorus with those charges so close to each other, a new type of reaction can happen that actually, um, basically decomposes thing. Entire structure. Okay, By the way, this tetra hydro Intermediate that I showed actually does have a specific name. You know what the name is? This might come up. This is called Obtain. Okay, what is the B 10 guys? So I've showed you so many weird words. Ill ID means that you've charges adjacent. Right? Be tame. Means that you have charges that are not adjacent. Right. So this would be a be tame because my charges air not adjacent to each other. Cool. So now you're waiting for the next step. So what's the next step? Well, guys, the next step is gonna be that my oh can actually attach to the phosphorus. Okay. So I can do something like this. All right. And now it's gonna take care of the positive charge again. And look what I'm gonna get. I'm gonna get something. Looks and intermediate. Looks like this. Oh, p h three p p h three Carbon metal, metal metal asshole. Okay, So, guys, this intermediate has another name. This intermediate notice. There's no charges so it's not a beating anymore. This is an Aqsa Foss 14 box of phosphate on. Okay, I'm pretty sure I'm spelling that, right. I might be, like, one vowel off guys. Spelling is not my forte, unfortunately, or go is, but I'm pretty sure that's right. Ox of phosphate. And it's this four Carbon are four member intermediate. Okay? And now, guys, we're finally ready to be done with this mechanism. What we're gonna do is we're gonna take the bond between the phosphorus and the carbon and make that into a double bond here. Okay, That's gonna make a double bond at the bottom. We have to break a bond. We're gonna break these electrons up to the O. Okay. And what this is going to give us that the very end. Check out what just happened. I just made a new double bond at the bottom. And what does that double bond have on it? Well, it has two methods on one side, and it has a method and an ethyl on the other. Why does it have a methyl and ethyl? Because I chose that ketone. I could have chosen any ketone I wanted, but that's the one I wanted. So that's the AL Keen that I guess this is my AL Keen product. And then you also get a byproduct with the phosphorus, which is really unimportant. And I'm not gonna even bother to name it because I'll probably get it wrong, but it's gonna be, um the P P H three bonded 20 negative. Okay. And that's gonna be a positive, And that's just gonna kind of go away. And the solution? I don't care about it. What I care about is that now I got my AL Keen. Isn't that so cool? So, guys, this isn't as cool as the box out method. I'll admit box out is the best because you could just put your ill ID. Remember which version this version of your village. You put that illit next, your carbon. He'll draw box, pretend like you can't see what's in the back. That's your all keen. But if you do have to draw the full mechanism, this is everything you need to know. Okay, this is literally you make the ill ID. You make the detain you do the nuclear book edition, make the detained make the Aqsa Foss routine and you're down to the AL Keen. Okay, awesome, guys. So I'm just gonna throw in one more little tidbit here. Okay? Which is that this reaction is not stereo specific. Okay, now there might be, there's research and there's there's literature on some stereo specific versions off of Wittig, but it's not confirmed, especially in your textbooks. Your textbooks do not talk about it being stared specific. So if there's a mixture of products, if you could make E and Z I summers okay, notice that in this case I would just get one product. But what if I could get multiple products? Will you have to draw both of them? You have to draw that you're going to get let's say this is one of them. Okay, so let's just say that I had ethyl and methyl on both sides. So then I would get that version, and I would also get this one. So if you guys recall if you have your large groups on the same side that Z and your large groups are on different sides, that's E. So you would have to draw both. Okay. Now, if you're Professor specifically says that he wants you to draw stereo specific version. By all means go for it. But the standard Wittig reaction is not supposed to be very stereo specific. Okay, Regio specific. Yes, you can choose which on what's on both sides, but not stereo specific. Alright, guys. So I really hope you found that video helpful. If you did let your friends know about us about me specifically, um, let's go on and move on to the next type of topic.

Determine the carbonyl and ylide that formed the following product.