Monosaccharides - Cyclization

Nucleophilic addition of the penultimate alcohol to the electrophilic carbonyl carbon leads to cyclization. This is the usual case. In the videos below we will refresh your memory on these terms!

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Monosaccharides - Cyclization

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Now it's time to dive deep on the most important reaction of mono sack rides. And that is cycle ization. So, guys, it turns out that in aqueous solutions, mono sack rights are most stable in their cyclic form. And Monta Sack rights conform stable five and six member ID rings. And those have different names. So a five carbon cyclic sugar is going to be called a farinos, and a six carbon cyclic sugar is gonna be called. The PIRA knows there are no four carbon cyclic sugars or seven greater because those aren't stable as rings anymore. So really the only stable ones you have to worry about our for a nose, and PIRA knows cool. So, guys, the nuclear feel like edition of the pen Ultimate alcohol to the Electra Philip Carbon Neil leads to cycle ization. Now it doesn't always have to be the penultimate alcohol, but usually it iss. So let me just kind of show you guys what we're talking about here. This is D glucose, as you guys should be well aware of. This is the penultimate alcohol. This is the Electra Filic Carbon. Remember that has a positive partial positive. So the nuclear feel like addition, meaning the O comes in attacks and kicks electrons up to the O. That reaction right there is going to cycle eyes this straight chain glucose in tow, One of two possible rings. Okay, now why would you get to possible rings? Well, the carbon you'll carbon if you think about the geometry of a double bond oven sp to hybridize carbon. It's tribunal plainer, right? It's tribunal plainer. So that means that it could be a top attacked either from the top or from the bottom, right? That oh could either come around the top and attack or around the bottom and attack. Well, it turns out that that is going to set up for stereo. I summers that air possible when these monos aka rights cycle eyes to different see one ep Immers are possible. Now what are we talking about here? Let's just go through this really quickly, Okay? The way that mono sacha rights are numbered is always from the one carbon being the point of attack being the carbon Neil. Because that's the top Carbon, this is C 2345 and six. Okay, we're numbering carbons right now. Okay, well after the cycle. Eyes, This is now going to be carbon one carbon to carbon three, Carbon four, carbon five. And this is actually carbon six. Right here. The oxygen doesn't get a number because it's not a carbon. Okay, so when I see that cycle ization leads to two different see one ep Immers. What I'm saying is that you're gonna have to different Kyra al it ease at one that are possible. And these two different EP Immers are actually specifically known as animals. So this is again this goes back to the very old, um, tradition of sugar chemistry that it has a unique names that are specific to sugars that Onley apply toe to carbohydrate chemistry. So you need to know that the specific eh, Palmer at the C one position, the two different positions are called an Immers. Okay. And what we have is the Alfa An imer that's possible. And the beta anim er that's possible. Okay, Now it turns out that the Alfa and, um er for specifically with d glucose, the Alfa anima is going to be the one that faces the O H down. Okay, meaning that the O must have attacked from the top because it attacked from the top and pushed the Ohh down. Okay, the beta an imer faces the O h up, which means that the carbon Neil must have attacked from the bottom. I'm sorry. The O H must have attacked the Carbondale from the bottom so that it would push this. Ohh! Up. Okay, essentially, guys, this Oh, here is the same as this. So is the same as this soap. So it's telling us a little bit about the mechanism and saying that it attacked from the bottom, pushing that Ohh up. OK, now, guys, I don't want you to be overly concerned with being able to remember that, okay? I'm just tryingto help it to make sense to you. Now, there is a very easy way to remember. What's the Alfa and, um er and what's the beta and, um er and that's what I wanna tell you guys. Now you can see there's some blank spaces. Okay, so this is the way it works. The Alfa An imer is the one that has the H trans to the stereo descriptor C five carbon. In this case, it's C five because that's the penultimate carbon of glucose. And remember that we talked about that. The penultimate carbon is the same as the stereo descriptor carbon. It's the one that tells you whether it's a D or whether it's an l remember that. So guys in this case noticed that my carbon five is faced up, right? It has a group that's faced up, which means that my Alfa animal should be the one that faces down because it's trans. Okay, now let's look at the other ring. The other ring noticed that my carbon five once again is going up. But the beta anima is the one that faces the an America oxygen sis to the stereo descriptor, meaning that should face the same direction. So it should also face up. Okay, so this is the way you can remember it that the stereo descriptor decides which one is Alfa and which one is beta trans to the stereo Descriptor is Alfa cysts to the stereo. Descriptor is beta. Now that we have that in mind, let's look at this reaction actually kind of take this all in. What we notice is that in obvious solution, very little of the mono sacharow I'd actually looks like the Fisher projection that we've been drawing the street chain really represents Ah, very tiny fraction of what the sugar actually looks like. The mono sacha ride is either gonna look like the cycle ized Alfa an Imer or the cyclist beta animal. Now, specifically for glucose. The beta animal predominates. It's about 64% of the beta an imer. And while 36% of the Alfa An Imer part of this explanation actually lies in equatorial preference, do you guys remember the principle of equatorial preference in cyclo hexane and how larger groups like to be equatorial? See how my O. H. Is equatorial? That is going to be part of the reason that this percentage is higher than that one because it likes to exist in the equatorial form. But guys, as much as I wish that was always true. There are exception to this and there are gonna be some sugars that actually prefer the Alfa animal for other reasons. So just based on this topic, you are not going to be expected to know which one is the major anner. Okay, All you need to know is that there are two different animals. You need to know how to name them and, uh, and how to draw them. Okay, that's really all I'm concerned about for right now. Now, let's also just take in the nomenclature, because the nomenclature has gotten significantly more complicated. So remember, guys that, uh, what what you guys know up to this point is that a D glucose is a glucose with the penultimate alcohol facing towards the right. But once it cycle, eyes is it makes a six member dring, right? So that means that D glucose now turns into d glue cope. Ira knows. Why is that? Because this stands for the six member dring, right? Six member drinking. Cool. Now what is the beta coming from? The beta comes from the anima. So this is how we name which anima it is. So the beta animal once again is the one that sis to the stereo descriptor and the Alfa animal over here is the one that's trance. So one thing is you're gonna notice is that the nomenclature is going to get more complicated as we keep changing the shapes of these of these mono sack rides. Cool. So guys, one thing that you might really be confused about and that you shouldn't know how to do at this point is to determine where the other O. H. Is air going. Because one thing that we've already discussed is that the an American Ohh can go either up or down because it's the C one ep immerse. Right? But what about this? Ohh. On to How did I know to draw it down and not up? How about this? Ohh! On three. How'd I know to draw up and not down where these? Where is this coming from? Where you're just supposed to memorize it? Guys, we have a system. It's easy. You're gonna be fine. Let's go ahead and learn it. The system is just a really simple, simple word that I used to describe it down. Right? Okay, So downright is just a random word. But it perfectly describes what we see on so the cycle ization of mono sack rides. So all you can think of about is that if the O. H. Is on the right of your mono sacha ride in the Fisher projection, then it's gonna point down in the ring. Okay? So if it's too facing towards the right, it's gonna point down. And that means that if it's facing left on the ring, it's going to face up in. I'm sorry. Left on the straight chain is gonna face up in the ring. So how does this play out? Let's erase a few numbers. So race a few. I'm just gonna try to simplify this. So this is my Ohh, that's important. Now let's number are other carbons. So we have carbon one, 2345 and six once again. And now we can go carbon by carbon. So to is to the right, which means that it should be facing down. And indeed it is. Three is to the left, which means that should be facing up and it is forced to the right, and that means that it should be facing down. And that's it. That's that's a Sfar. A czar rules get you to your last won the penultimate won. The stereo descriptor does not follow that rule. So how do I know what I'm going to face it up or down? Well, the penultimate one has a special rule, which is that I have right here your stereo descriptor. If it's a D sugar, it's gonna face up on the ring. So if it's a d sugar, it's gonna face up. And what did I tell you guys about D sugars? There is the most common. Almost everything is gonna be a D sugar. So in this case, was this a D Sugar? Yes, it was. It was a D sugar, which means that my pen ultimate one here should face up. If it had been an El Glucose, then it would face down. That's where the rule comes from. For your penultimate or stereo descriptor carbon. Once again, guys, I don't want to confuse you. I put your C five. That's Onley for this example because it happens to be a hex. Uh, heck sauce. But if it had been a smaller, um, model sack ride, then it would not be C five. It would be whichever one is the penultimate, the last Cairo carbon, the stereo descriptor. Okay, So, guys, um, just one more thing that I want to give you a preview of before we move on to the practice problem, which is that the process of turning a straight chain into a ring is called cycle ization. But then there's an opposite process that we're going to discuss more later called Muto Rotation. What is Muto Rotation? Mutual rotation is the ability of one animal to turn into the other animal by going back into the straight chain. So mutual rotation would be a smaller process where Beta turns into Alfa and then we're Alfa turns into beta by going through the strait chain and shuffling the O. H up and down. Okay, cool guys, let's move on to a practice problem.

Problem

Draw the β-anomer predicted through the cyclization of D-mannose

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