We know that monosaccharides have the ability to react at the –O position in several different ways. In acidic conditions, monosaccharides can alkylate at the anomeric position to produce o-glycosides.
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in this video. I want to teach you guys the most important oocyte reaction of mono sack rides. And that is called Oh, glad cost Sedation. Alright, guys. So, as you might or may not know, mano sack rights have the ability to react at the O position or the oxygen position in several different ways. Okay, but in acidic conditions, monos, aka rights, can calculate selectively selectively at the an America position to produce what we call OGE like asides. That means, um, this time upon here, it's an ass. It'll where you have in our group specifically attached on Lee to the opposition. That's called a glucose side. It gets an O side ending. Okay, this process is also known as Fisher Kost sedation, and it actually has a lot of similarities to another reaction that you might have learned with, uh, with Fischer's name on it. Fisher s terrifically ation. You guys remember that? It's very similar because it proceeds through a reversible intermediate. And, um, it's acid catalyzed. There's oxygen and carbon is involved. It's not a very wild mechanism. So once you get it, it's gonna be pretty easy. Okay, Now let me show you guys, the general structure, the general formula here. General reaction is you take a beta d Google pira nose and you reacted in alcohol and acid. So when I said it's similar to Fisher A certifications because that's the same thing that you would have used for a carb oxalic acid, right? It's the same principle of that. You're using acid in alcohol with a with a carb oxalic acid. Let's say and remember that for Fisher s terrifically ation, you would get a Esther right? You would get O. R. What's the same thing that happens here except that it's specifically on Lee happens to this O. H. And it turns that ohh into an O. R group that has the same our group here. But it's also, since it's on Lee at the America Carbon. You're going to get a mixture of animals, obviously due to mutual rotation. So you're going to get some kind of combination of Alfa and beta animals, depending on the specific mono sack, right? And what, which one is preferred for that setting? Okay, at the end, what we get is a new functional group called in a Settle because you have O R groups coming off of both positions O R O r. And if it's an a settle that specifically once again gets the name of OGE like aside because it specifically has an art group at the an America position. Okay, so you might be saying, Okay, Johnny, I'm getting what you're saying, but how can you guarantee that it's on Lee gonna happen at the an America Carbon? Why doesn't it happen here or here or here? Well, guys, the reason is gonna lie in this intermediate called an Oxo Carbon IAM Intermediate, which is a very special intermediate. It's the important intermediate of this reaction. And that's what I'm gonna show you in the next video. In the next video, I'm gonna prove to you guys how this can Onley happen at the an America position and it can't happen anywhere else. So let's go ahead and go to the mechanism
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Okay. So as any good acid catalyzed mechanism would go, the first step has to be pro nation. And this case, guys, you might notice that the acid I'm using is just gonna be, um are a wage positive because its's an easy combination of my alcohol, plus my acid, it makes it easy to work with. Okay? And it's gonna have a very easy conjugal based. So that's what we're gonna use. Okay? And guys, because of the fact that we're trying to get rid of the an America alcohol, right? We're trying to turn it into an O. R. So that's what we protein eight. We always protein ate the thing that we want to leave. So my first step is just to take this ohh and use it to grab a proton from my asset. What that's going to do is it's going to create a good leaving group and in the next step, I can eliminate that leaving group by using one of the lone pairs on this 01 of these lone pairs is going to come in, make a double bond and kick out the water. And what that's gonna make is an intermediate that looks like this with a positive charge here. Okay, Now, guys, this is the Oxo Carbon IAM cat ions. Let's go ahead and redraw it at the bottom so we can show the residents structures. There's a dull bun here with a positive charge. And we know that there's another resident structure that would put these electrons up on the, uh Oh, meaning that I'm going to have a positive charge here. Okay, These are the two resident structures that are possible for the Oxo Carbon IAM Cat ion. And by the way, this is why this mechanism can Onley occur at the one position. Because notice that if we were to let's say, do this at the two position right here, we would not have any oxygen that we could form this resident stabilized intermediate with the only way that you could get the residents stabilized Intermediate is if you're next to the oh, and this is the Onley alcohol that's directly next to an Oh, so that's why the an America position is the only one that can do this mechanism. Okay, so now we have this resonance stabilized Carvel Cat ion. And now is the time that we can ads, you would take your R o h. Whatever you're trying to add Thio like hostilely and it's going toe attack the positive charge. So now what I'm gonna get is squiggly line. That's the ugliest squiggly line. Let's try a little harder squiggly line. R O H r. Positive. The reason I keep putting squiggly line guys is because I don't know if it's going to be Alfa anima or beta anima. It's gonna be something in the middle, not something. You know what? It's gonna be an equilibrium of the two. And then finally, we could use our conjugate base too Deep protein eight, and give us our final answer, which is just O R. Okay, so, as you guys can see, um oh, glide Kasid ation selectively ads in a Seattle group or in our group specifically to the an America position and no other positions because no other positions would give us this very important Oxo carbon iam cat I am that is resonant, stabilized. Okay, awesome guys. So I hope that made sense. Let's move on to the next video
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