Aldol Condensation - Video Tutorials & Practice Problems
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An aldol reaction gets its name from the 2 functional groups that make it up. Let's take a look at how we can distinguish this condensation from others.Â
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Hey, guys, in this video, I want to focus in on a specific type of condensation reaction called on out all compensation. So from prior videos, we know that in Italy is a negatively charged species and it can attack Electra files. Okay, But what we didn't really realize up until this point is that thes anil eights can actually react with themselves. Okay? They can react with themselves to condensate, specifically, If it's a key tone or alga hide, it's gonna condensate into this category of molecule called a beta hydroxy carbon Neil. Okay, now the final products are called al dolls. That's the reason that we have that name because they're part Aldo Hide. And they're part alcohol. Okay, so that hence the name Al. All Okay. So, guys, what I'm gonna do here is I'm gonna show you the full mechanism for an algal condensation. And one of the most important things to realize about any condensation reaction is that a big part of getting these questions right isn't just knowing the mechanism. It's knowing how tow line up your carbon eels. Because if you line them up incorrectly, you're gonna be doing a lot more work and you're probably gonna get it wrong. So I'm gonna teach you not only just the mechanism, but I'm gonna use my years of teaching experience to try to ingrained this method into you of how is the best way to line up your carbon deals so that you can always visualize the product the easiest. Okay, well, the first step, guys is super easy. All it is is that you're using some kind of base, usually O h negative to pull off a proton and make your family. Now, remember that emulates have two different resident structures. There's also resident structure with the negative on the Oh, but we're not gonna use that one for this mechanism. You always wanna be using the Italy on the carbon because that's gonna help predict what our product looks like. Okay, now, the reason that we were getting Aldo compensation is when you have a base. But you have no Oops, that's not No, no, you have no other a lecture file. Okay, so I'd be wondering how would I know that something is an algal on? How would I know that something is? Let's say, a reaction from another chapter because There's a lot of re agents that you know now. But guys, if you are forming and Italy without an electrical to react with, then you know this is gonna be a self condensation, which is exactly what we're gonna draw. Okay, so we've got our finally noticed that my family, I'm drawing it on the left hand side. I'm always gonna draw the usually on the left. And I don't have an electrical on the right. I don't have a hey light or and a seal chloride. Whatever. So that means I'm forced to react with just another carbon Neil. Okay, well, how does that work? Well, I like to call them. There's the Emily, and there's the Electra file. Why? The Emily is the one with the negative charge. The election file is the one that you're gonna attack the partial positive of. Now, this one should not be in an email late for you should just draw this the normal way that it was before the base reacted. Okay, now, a few other pointers here, you wanna make sure that your family is drawn on the left, but that you're an eye on is toward the electric file. Okay? Because you wanna have the electrical and the anti on is close to each other. So here I'm joined the evenly on the left, But I wanna make sure my native charge is as close to the electric file is possible. Okay. Also, any are groups on it face downwards, and this is gonna come up more later. But if I had bulky are groups on that ch two, I should actually face them facing down to clear the way for the electric file that I'm about to attack. Okay, awesome. Now my lecture file, you've actually got some special rules about that one. The electrical you draw on the right. Okay. Always on the right. And you should draw your, um, smallest group toward an eye on. Okay, The reason is because we're gonna have to attack with the anti on, and it's best it's gonna be easiest to visualize if I have my small group close to the anti and my large group away from it. Okay, um, I think that's enough to get going. Okay, so this mechanism is gonna look like follows. Okay, This is a nuclear filic edition mechanism. So my negative charge is going to attack my partial positive I'm gonna break up on and guys, I'm gonna make a tetrahedron. Intermediate Now it's a big tetra. Usual intermediate. I understand, But you still have on own negative with now. What groups? Well, now you've got the extra siege to that's attached here. We still have that h the h that was here is still here. It's just I'm not drawing it. And then there's the ch three. Okay, now, this is called a nuclear Felix addition mechanism because we're gonna protein eat the o at the end. We're not gonna kick out a leaving group, so we use water or acid tau protein eight, and to give us our beta hydroxy carbon Neil. Okay, because I have a beta hydroxy on my carbon deal. Okay, Now, the reason I call it Carbon Neil is because it could be either ketone or an alga high, just depending on what you started with. Okay, so that's really it. It's a really easy mechanism, its nuclear filic addition putting two molecules together. One thing that I always encourage my students to dio is to count up your carbons at the end because the carbons in your product should match the carbons of your original until eight times two. So my original easily had How many carbons to So I have two carbons here I'm gonna put to see right. I'm adding another to see right. So that means that my beta hydroxy Carbonell should have If I did it right, it should have foresee, does it? Let's count. 1234 Yeah, we did it right. You'd be surprised how many stupid mistakes were made because you miss a carbon. Are you at an extra carbon? And guess what? Professors are not forgiving on that kind of stuff. Okay, you can You can make a lot of mistakes, But you can't miss carbons because it's just a completely different molecule. Alright, guys. So now it turns out that beta hydroxy carbon heels are a little more complex. They it doesn't just the story doesn't just end there, okay, because beta hydroxy carbon eels are much easier to dehydrate than the typical alcohol. Now remember, this comes from this concept comes from organic chemistry one where alcohol's underwent dehydration reactions. Remember that in a dehydration, I take away of water and I get a double bond. Okay. Now, usually you need heat to do that. Or you need a lot of, you know, a very good strong acid. Like usually be an acid catalyzed dehydration. I don't talking a lot, so I'm gonna write it here. Usually, this would be an acid catalyzed dehydration. In order to do this, I'm gonna put here usually. Okay, but it turns out that this alcohol, this specific beta hydroxy, is not going to require a strong acid to dehydrate. In fact, it's not even going to require heat. Okay. Why? Because look at the conjugate. Look at what happens. Not the country, but look at the product after you dehydrate. The dehydration product is uniquely stable. Why? Because it's conjugated. So do to conjugation. This double bond is much more stable than normal double bond. What that means is that it's not going to take much for that alcohol toe leave. In fact, it can leave both in acidic environments and in a basic environments. Okay, In acidic environment, it's gonna leave via an e one mechanism. So you guys remember that's a Carvel cat ion mechanism where you wind up forming carbon carrion and doing a beta elimination. In a basic environment, you can't get a car, Will Catalan? You would actually react by another mechanism that we're not even going into in this course called e one C B or E one conjugate base. Okay, now, the point here isn't for you to draw these mechanisms. That's not my goal. Right now. What I want you to know is that many times because this dehydration is so favored, we're gonna assume that the condensation product dehydrated on its own without even requiring an explanation. Okay, so sometimes you're going to see your professor. Just write the product as a double bond as a dehydration product, and you're not gonna ask questions. You're gonna say, Professor, why did dehydrate guys these air gonna spontaneously dehydrate? Because the product is so stable. Okay, now we do need to know what this product is called. It is in general to dehydration product, but specifically as two names one and most commonly told an Alfa Beta unsaturated. That's because now we have an unsaturated bond between our alfa and beta carpets. Okay, so alphabet unsaturated keep that in mind. Another really important name for it is an e known Okay, so in in, um, just makes sense. It's a combination of al, keen and own that would either come from the key tone or the alga hide. It's still it's a carbon e. Okay, so that's where we get the word e known from both of them are interchangeable. They just mean that it's the dehydration product. Often, Aldo condensation And many times, for example, when I'm drawing my products for all of my practice problems, I'm always just gonna be taking it to the No, I'm gonna be assuming dehydration. And for your sake, if you're watching these videos and you're wondering, what should I do? Should I dehydrate? I would always dehydrate unless you professor says not too okay. Because, like I said, it's so favored. That's just gonna happen without a lot of stimulus. Okay, awesome guys. So that's it for this video. Let's move on to the next one
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Problem
Problem
What product can be isolated from the following aldol condensation reaction?
A
B
C
D
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Problem
Problem
Provide the mechanism for the following transformation.
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