Organic Chemistry

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24. Carbohydrates

Monosaccharides - Wohl Degradation

The Wohl Degradation is a chain-shortening reaction. In this type of reaction, the aldehydes are transformed into cyanohydrins first to be reversibly removed by base



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Hey, guys. Now we're going to discuss a reaction that is essentially the opposite of Kill Janni Fisher. Chain lengthening. And that is the wall degradation, which is a chain shortening reaction. Let's go ahead and look into it. So, guys, as I mentioned with Kelly Anne Fisher, Aldo Hide, Aldo Aldo hides are susceptible to the same exact carbon you'll reactions that we would have learned in our alga hides and key tone section. And scientists realized a long time ago that they could strategically take advantage of that Aldo Hide group to do really to do the same types of reactions that we would have done in carbon oh, chemistry. But for purposes that are specific to sugar's OK, so what did I tell you guys about Sino hydrants? You can use Sino hydrants, toe add carbons in Killian Fisher, right? But I also told you that siamo hydrants are reversible, E added, So it is possible toe actually take them off after you've put them on. So opposite to kill Janni Fisher. In this type of reaction, which is called wall degradation, the alga hides are transformed into cyan a hydrants to then be reversible e removed in base. So the idea is that we're making Sino hydrants again. But for the opposite purpose this time we wanna put them on so that we can take them off and remove a carbon. Okay, Now, the chain is gonna be shortened by one carbon at every cycle of wall degradation. And theoretically, you could keep shortening the chain until you run out of alcohol group. So just like Colleoni Fisher, you could just keep shortening that chain. Okay, Now, one big difference between Colleoni Fisher and Wall degradation is that because this is a change shortening reaction and not lengthening, you're not going to create multiple multiple EP immersed. In fact, the wall degradation is always going to result in a single Epivir products. So notice that there are no squiggly lines here. We know the exact stereo chemistry of every alcohol because all the stereo chemistries retained, which I'll show you in a second. Okay, Now, the reason this happens is because in Kelly Anne, I'm sorry. In wall degradation, the C two stereo center is lost a every cycle. Now, what am I talking about? I'm talking about second carbon. That would be this guy, right? here. Okay, Notice that right now, that is a ohh that's facing towards the right directions. That is in our configuration. Right. But what we're gonna do is we're actually going to at the end of this reaction, turn that carbon into an alga hide. So is it still going to be Cairo after the fact? After you've done the wall degradation? No, it used to be Tyrell, and now it's gonna be a Cairo. So what that means is that it's possible for multiple sugars to produce the same product. Because, for example, if I reacted the wall degradation with an O. H that was faced towards the right on the sea to position and then I also did a wall degradation with another sugar That was the same exact sugar. Except that the O. H. Was faced towards the left, sort of the opposite C two FM. Er, if you reacted with both of those ep Immers, you'd get the same exact product because regardless of which, when you started with, it's gonna turn into an alga hide. Okay, Now I know that I've been just talking a lot. Now I'm going to go into the mechanism, but we are gonna practice this concept later, so don't worry. We're gonna come back, and I'm gonna show you guys how multiple sugars could lead to the same product using the wall degradation. So what I want to do now is really just go into the re agents because I've been talking too much. So first of all, let's start up with D glucose de Glucose. The very first step is that we're going to turn it into an aiming derivative. Now, what we're gonna do here, guys, is we're gonna take advantage of the fact that in Carbondale chemistry, what did we learn about ketones? And Aldo hides that if you react them with primary means, let's say N h two are right. So it's a primary Amine, what are you gonna get as a product? This is a review in review of the section of carbon chemistry called in means you could search for it in your search bar if you want. What you're gonna find is that this becomes a double bond end and a single bond are okay. And this is what we called an Emmy, right? But then we also talked about in that section how If you have a Z group instead of the our group So instead of n h r, imagine that it's NH two Z, meaning it stands for something electric negative. Something like Ohh Okay, then the product instead of being, um I'm sorry. Instead of being an r, it's gonna be end Z okay. And guys, that Z is going to be the hydroxyl group in this case. So specifically, the primary amine derivative that we're using is called hydraulic salami. And when you react hydroxy linen, which is having the O. H with a alga hide what you're gonna wind up getting is an Emmy and derivative. So this is called in. I mean derivative. And specifically the Indian derivative is called an oxen. Why is it called a knock? Seen that the specific name that we give to the Indian derivative of hydraulics Olympian and all of this is reviewed in your Imean derivative section of clutch. So if you want to just type that in to go over these reactions again, that's fine. But I'm just like, you know, this is all you need to know. That you go from the first step is to go from your sack ride, and then you make an oxen, which is really just in type of Imean. Great. Now we have our oxen. This is all review. The next step is that we actually want to rearrange that ox seen or that it means derivative into a scion. A hydrant. Now this reaction is a reaction that I don't expect you to know as well because it's a much It's a much less emphasized reaction in organic chemistry, and it's called the Beckman Rearrangement. Now, guys, the Beckman rearrangement is not unique to the wall degradation. There are other reactions in organic chemistry that use the Beckman re agent rearrangement. But it's just one that we don't focus on as much as we do. It means so I'm not gonna make you. I'm not gonna hold you accountable to no this reaction Very well. In fact, what I want you to do more than anything is just memorize what happens in this step. And what happens in this step is that we use and then hydride, this is the formula for anhydride, remember? And hydroids, we're going to use it anhydride to dehydrate that oxen and rearrange it into a night trial or a scion of group. Okay, so this is basically a rearrangement that I'm not gonna hold you accountable for this mechanism. Your professor won't either. Not in this section. You don't need to draw the whole rearrangement. You just need to know that that oxen is going to rearrange to assign a hydrant. Okay, now, here's the cool part. We learned that Sino hydrants add reversible e. So that means that it's possible toe also kick them off if you use base. And that's going to be our third step. Our third step is going to be used to use a strong base, usually meth oxide. Um, and what we're gonna do is we're going to reform the carbon deal and kick off the scion a hydrant which will eliminate one carbon. Let's see what the mechanism would be. It would be negative, grabs the h from sea to then those electrons from the own the H turn into a carbon, Neil. So now I'm gonna get a double Bondo, and then I'm gonna kick out my CNN, okay? And guys, I put here, This is an Alfa elimination. Not because I want you to memorize it, but because I want you to know this is an elimination reaction. Technically, what we're doing is we're getting rid of two single bonds and we're making a double bond, which is the definition of elimination. You get rid of two single one to make one double one. But it's not the same as beta elimination, which would have been in Oracle one. Remember you had e two and stuff like that. This is not that it's just a different type of elimination called Alfa Elimination, because it all happens on the same carbon on the Alfa Carbon. Everything takes place. And anyway, guys, we wind up getting, and this is really the most important part of this whole thing is you wind up getting a mono sack ride that now, instead of having a hydroxyl group at the sea to position that see to position became an alga hide and we lost h c n. Okay, so basically we lost h c n and we got this in return. Okay, so now this specific mono sacra I would be called De or Aba knows why? Because notice that the Chire ality of all of these Kyle centers has to be retained. So this is gonna be the same exact mono sack right is the only started with, except that we chopped off the very top carbon. Okay, so that's the wall degradation. Does that make more sense now, guys? So basically, wall degradation is all about using this Siris of re agents to chop off the very top carbon. And what that means is that we're going to get a stereo specific product. Okay, Awesome, guys, let's go ahead and move on to the next video.


Which aldohexoses produce the same Wohl Degradation product

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circle the Aldo Hex doses that would produce the same wall degradation product. If none of them would share a degradation product, then just right. N a quote. So, guys, um, remember that what we're basically discussing here is that wall degradation is going to get rid of your seat to stereo chemistry. So whatever that C two is gonna be gone, and all you have to look at is what's below sea to that's what's gonna be retained. So since these air all l'd Aldo heck, so says I would expect that after wall degradation, all these carbon eels disappear, right? So those cardinals, they're gone, they turn into CNN groups or H c n. And then all of these oxygen's become carbon heels. Let's turn them into double ones. Right now. This is gonna be a little bit like makeshift, but it's gonna work. Just put double ones. Double bond, double bond, double bond, double up on. Okay, now, keep in mind, guys, what is the stereo chemistry of this carbon now? Once it has a double juan tribunal plainer, so it doesn't matter what side the O double one always facing. It doesn't matter because it's tribunal plainer anyway, so those are the same thing. There's free rotation around that single bond. Does that make sense? So it doesn't matter. It could be the same if it's towards right or towards left another thing to keep in mind, I'm ignoring the H because it's going to eventually leave. So, like this H would eventually go away. So I'm literally just saying, without a mechanism, withdraw carbon eels. Cool. So if all of these were the same, all those all the heights left and if all those carbon eels they're the same at the top, which of these two are identical? Do you see any two of these that are identical sugars? And yeah, I do. I see glucose and manos glucose and manos will become the same exact mano sack cry because the top carbon was gonna leave and then they're just both going to turn into a carbon meal at that position, the blue position, and then all these other groups were going in the same exact directions. Okay, so that's actually the answer that manos and glucose produced the same exact wall degradation product because the fact that there si two members of each other and see to embalmers are lost. The stereo chemistry has lost Every time you do a wall degradation cool. Um, of course, that's the end of the question. Let's move on to the next video.