Directed Condensations - Video Tutorials & Practice Problems
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So far condensation reactions seem pretty straight forward. But, let's see what happens when we have an asymmetrical ketone.
1
concept
Directed Condensations
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Video transcript
Alright, guys. So hopefully by now, the Aldo condensation is starting to make a little bit more sense. But what happens when you have an asymmetrical key tone that presents a problem? So whenever you're reacting and in a late mediated reaction on an asymmetrical key tone, two inlets, maybe possible. So we're gonna have to use a directed reaction, okay? Directed reactions or what we used to pick the inlet that we want. Because if you only have one choice of immolate, then you're in Italy is gonna hit your electric file and you're done. But what if you have two possible immolates? Then which one is the one that attacks the Electra? Philip Carbon? Who knows? Well, that's what we have to use thermal dynamic versus kinetic control. So, guys, the thermal dynamic Italy, we've learned this before, is the more substituted one. Okay, it's gonna be favored by small bases. Okay. Whereas the kinetic Emily is the less substituted, one is the one that's easier to reach, and it's favored by bulky bases. Okay, so what that means is that if I want to run an Aldo reaction, let's say, on the right side of my key tone here. I only want to attack with the Italy on the right side. Then I would use a small base, for example, any ohh okay. Or any other small base. However, if I wanted to react on the left, substituted side of the ring, making my family on the left side and then having that attacking Electra file thin, I definitely have to use a bulky base. And for that, we've got two options but the most popular for this chapter being L. D. A. Because of the fact that it's a non nuclear feel like base. So we don't have to worry that it's going to actually add to anything. It's just gonna remove Ah, hydrogen. Okay, but also Turkey talk side would be a possibility. Excellent guys. So now go ahead and try to predict the product for the following reaction, and then I'll jump in
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example
Predict the Products
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Okay, So what base was this, guys? I hope you didn't get tripped up on that because I've drawn this for you already. This is just another way to represent L. D. A. Right L d A stands for lithium di isopropyl a mydd. And that's what we have appear. Okay, we got the two isopropyl groups. You're negatively charged and and your lithium associate with it. Okay, So where is my only gonna form, by the way, another question. Let's back up, Hold up. We know this is in the al doll section, so you're obviously thinking along that lines. But how would you know that this is even an outdoor reaction? We've got L. D. A. And a key tone. How do I know what to do? Remember I told you guys that anytime you have a base plus a ketone, let me let me re arrange that any time that you have a carbon eel like an alga hide or ketone this important guys, plus a base, okay. To make the easily plus no other electrical. Okay, that's gonna be and Aldo okay, because what that means is that you're gonna form. And in a late but you're not gonna have an electric fall to react with, so it's just gonna have to react with itself. Okay, that's exactly we have here. We have a key tone with L d. A strong base gonna make Anita late and no other Electra file. So I would make my family on this side. That means that the less subsided side, there's a directed reaction. I'm gonna have to flip this thing in order to use my rules of how to set up a algal. Right. So let's go for it. So remember I told you, as they always want the Emily facing the anti on towards the right. Okay, so I would twist that around that my anti and is facing what's gonna be the Electra file? My Electra file. I want to draw with the smallest group facing towards the anti on. So I would keep it just as is Okay, we're good to go. We're good to do our first mechanism. So my negative attacks the oh, kicks up the electrons. I wind up getting something like this where I have a molecule that looks like this carbon now that is attached to trying to use green that is attached to That's the new bond. And that is attached to what? An own negative. And this thing and the metal group. Okay, so what's gonna happen here? Well, um, the basically the conjugal of L d. A. So remember, L d d protein ated. Right? So the kanji could protein ate this. So we're always going to get a pro nation you're never gonna is gonna be stuck at the touch of usual intermediate. You could always use at least the hydrogen that you took to replace this. So I'm just gonna put h plus because I know that there's a t least one hydrogen hanging around since I took it off. Okay, What this is going to give me and I ran out of room over here. So by the way, these air all reversible arrows, guys. Yeah, What this is going to give me because it's gonna give me a molecule? Looks like this. Okay. And that is one of the final answers. So we're done. Good. That's the beta hydroxy carbon, Neil. But guys, I told you that I'm gonna be spontaneously dehydrating these guys. Why? Because that just seems to be the thing to Dok. It's gonna make us very stable, um, product. So let's just spontaneously let's dehydrate this thing and be done with it. Also, we have strong base around, so there's a justification. So when you dehydrate, you always dehydrate between the Alfa and the beta. Okay, to make an Alfa Beta unsaturated So then I would draw it like this. My final product. Okay, this is my Alfa Beta unsaturated and it's also called an unknown right, Awesome guys. Now, actually, one thing that I didn't get to mention for the general mechanism of Haldol that I'm really glad that we're talking about here. Okay, which is that guy's Aldo is reversible reaction. So you can turn a key tone into a beta hydroxy carbonell and it could go back just fine, depending on equilibrium conditions. But there's one irreversible step. The irreversible step is dehydration. Once you dehydrate, you're not going back. You're not getting alcohol. And guys, that is the reason why Another reason why the dehydration product is the predominant product. Because once you achieve it, you're never going back, so it keeps getting removed from solution. So you can imagine that over time you're gonna have 100% dehydration product because you keep removing that region from the solution as you create it. So eventually, even if it's a slow reaction, you know the rate is slow. You're still gonna generate ah higher and higher yield that dehydration product until everything has dehydrated. Okay, so it's stable because it's conjugated. But it also happens to be a final product because it's an irreversible step of the reaction. Okay, so if that makes more sense as to why I'm gonna be dehydrating these compounds. Awesome guys, you did great. Let's move on to the next topic.