19. Aldehydes and Ketones:Nucleophilic Addition
DIBAL
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Why LiAlH4 doesn't work
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Hey, guys. So in this video, we're gonna learn how to make all the hides through reduction. So at this point of the course, you've definitely seen a carbon Neil coupled with a reducing agent. And what we're used to seeing as the product of a carbon eel and reducing agent is alcohol's. Okay, we have been dealing with very strong reducing agents up until this point. The two that come to mind for me when it comes to carbon eels are lithium, aluminum hydride and sodium borough hydrated, thes air to reducing agents that you've definitely seen by now. And they're both really good at making alcohol's from carbon eels. So in this specific example, we would actually want to use LH or lithium aluminum hydride. You guys might remember that this one is the one that works better with Carl oxalic acids. And what winds up happening is that it adds to equivalents of hydrogen to the carbon eel to get alcohol. No, this is great. But what if we want to stop with one equivalent of hydrogen? What if we don't want to go all the way to the alcohol instead? We want to just go to the al hide first and stay there. Well, if that if we if that's our goal, we're gonna have to use some milder reducing agents because we're gonna have to use, um, reducing agents that don't want to go all the way to the alcohol that don't wanna add to equivalents and just are okay with adding one equivalent of hydrogen instead. Okay, So what we're gonna do now is we're gonna learn to such free agents that would qualify as milder, reducing agents that actually make alga hides, not alcohol's man. We're going to see if they have some things in common in terms of the fact that they use Derek Hindrance Thio reduce the power of the reducing agent. And they're both gonna add on Lee one equivalent hydrogen each time. Now, these regents do seem kind of random, So they've got some weird names. We're just gonna try our best, and I'm gonna hope to help make it flow. Okay, so let's go ahead and start off with the first one
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LiAl(ot-Bu)3H on Acid Chlorides
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So the first new region that we're gonna learn specifically works with acid chlorides and it turns acid chlorides into Al decides. Okay, this re agent has a really long name, but all it is is it's hysterically hindered version off lithium aluminum hydride. Let me draw it out for you. It's actually starts off exactly the same l i ale. But then this is where it gets weird. Instead of having four hydrogen, three of those hydrogen are replaced with what we call Turkey Toxie Group. So then we drop parentheses. E um so trying to see oh t view three h. So as you can see chirpy Toxie groups because I basically have ethers made out of these o t beauty groups and then I have only one hydrogen left over That's actually gonna react the other ones don't the other groups don't. Okay, so this molecule, even though it looks really complicated, it's just gonna be a version of lithium aluminum hydride that adds one equivalent. So I'm gonna get Aldo hide instead. And what I want you guys to draw on this blank up here is just that. What's the thing that's making it hindered? Well, that we've got these oh, t beauty groups times three. We're adding those to the LH to make it. Ah, lot less reactive. Okay, so that's the first one. Unfortunately, you do have to memorize this. You have to memorize how to draw it and what it works with. It specifically works with acid chlorides. Okay, so that's it for that one. Let's move on to the next free agent.
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DIBAL-H on Esters and Nitriles
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So this next free agent is also kind of random guys. It works with Esther's, and it works with night trials. Let's draw that. And what it's gonna do is it's gonna turn esters and night trials into Alba hides by adding on Lee, one equivalent of H. The name of this region is weird. It's called Deibel H. And what the heck does that stand for? Okay, so die about H The long name. I will give you the long name. It's called Die I so beautiful. So that's the die, right? Aluminum hydrate. Okay, hence the name die bowel h All right. And this re agent is a pretty big stare. Ecclesia hindered reducing agent that's gonna work with these two functions groups and it gives us Alba hide. The only thing I was gonna do extra I mean, really, we just have to memorize it. I'm not going to show you the mechanism, but I do want to show you the way it looks. So it's just gonna be a nitrogen. I'm sorry. Not a nitrogen and aluminum. An aluminum with di isil. Beauty groups attached to an h. Okay, so again, you can see what I mean by seriously hindered is a beautiful groups are pretty big. It's got two of those around. Okay? And that's going to influence its reactivity now. One second. One last thing about this regent it does also require Ah, hydraulics step. Okay. So typically you'll see it written as devout h and then to water water is required to hide, relies the intermediate and make it into the final. Al died. Okay, so now you guys know the two new reducing agents for this section. We've got hysterically hindered version of of listening. Will hydrate is one of them. And we've got Di Bell. All right, so let's move on to the next topic.
Additional resources for DIBAL
PRACTICE PROBLEMS AND ACTIVITIES (5)
- Predict the major products of the following reactions. (c) < of reaction>
- Show how you would synthesize octanal from each compound. You may use any necessary reagents. (d) 1-bromohep...
- Show how you would accomplish the following synthetic conversions efficiently and in good yield. You may use ...
- Show how you would accomplish the following synthetic conversions efficiently and in good yield. You may use ...
- Predict the major products of the following reactions. (b) < of reaction>