Mutarotation

now I want to dive deeper into the process by which an Alfa and, um er can become a beta and, um er and so forth. So guys, pira nose and furnace rings are constantly hide, relies ing back and forth between their cyclic and straight chain forms. Now you guys know what that mechanism looks like. You know what the rings look like. And I'm here to tell you that it's in constant equilibrium. It's not just like one ring gets formed, then it stays like that. It's a constant equilibrium of hydraulics. ISS cycle, ization de cycle ization, etcetera. Okay, well, the specific process by which in an America position would convert between the Alfa and Beta forms is called mutual rotation. It's basically the backwards reaction of cycle ization, but it's so that you can achieve the other animal. Okay, now here in this example, what I've done is I'm showing you how Let's say you start off with a beta d glue go pira nose and you expose it to either acid or to base just a little bit of acid or just a little bit of base. This, uh, bring is going to start is going to begin to hide, relies and it's going to turn to the straight chain. And then it's going to eventually Muto rotate, forming the other animal. Now what I did in this drawing is I didn't draw just the Alfa Animal. I actually drew this squiggly line. What does that squiggly line mean? It means that you lose the Alfa and beta and, um er information because you're going to get some mixture of both. Now it's important to note it's this is not gonna be a rasam eight. Remember what rasam eight means? It means that you're gonna get 50 or 50 of each. I'm not saying that that's not what the squiggly line means here. It just means you're going to get a combination. So here, instead of putting beta d Google Para knows, I just put d Google paranoia because you're gonna get a mixture of the two mutual rotation is gonna make it so that you're just gonna have some kind of mixture of the two. So, guys, it turns out that in your textbook, the explanation of mutual rotation is very, very closely tied with this idea of optical activity. So what I want to do is instead of having you read that and be confused, I just want to explain it. So you can understand why they always talk about optical activity when they talk about mental rotation. And what it is is that optical activity provided the proof for mutual rotation, which I'm going to show you now. So, first of all, it's important to note that animals are always going to default differ in optical activity. Okay, You're always like an Alfa animal is always going to rotate light different than a beta animal. Okay. For example, the Alfa animal of a de Google pira knows rotates light at a positive 1 12 rotation in a polar emitter. Okay, whereas a beta d Google PIRA knows rotates light at positive around positive 19. Okay, guys, these air super random numbers that you do not need to memorize. Okay, but this just shows you the completely different optical activity of the Alfa versus the beta. Now, if you weren't paying attention, and maybe you just kind of it's like thought thought very quickly. You might think you might wonder why really not just opposite rotations? Because remember that back when we talked with optical activity back a long time ago, we talked about how, if one in an steamer shows the positive rotation, the opposite in and humor should then show the negative rotation of that same rotation of plane polarized light. In this case, they're both positive, and they're very different from each other. Why is that? Well, guys, remember that And animals air not finance humors of each other, right? They're not in Ann Summers like, ah, bunch of the Cairo center stayed the same. What they actually are is remember their diets, stereo MERS. Okay, so that's why they have unrelated activities. You can't predict that one is going to be positive. One's gonna be negative. They just have random numbers here. I've given you the random numbers for glucose PIRA knows, but other types of rings you would need to actually use a pole or emitter to get that number. Okay, so it's not something that you're supposed to memorize now. Why is this important? Well, because back in the day when they were first discovering kind of this relationship between optical activity and Chire ality, it was noticed that it was observed that d glucose pira knows always equal liberated to a positive 52 5 rotation, which is weird because that's not the rotation of either one of these. Right, 112 is one. The other one is 18.7, and somehow it would always rest. If you let it sit around long enough, no matter which one you started with, whether you started with 100% of the A or whether you start off with 100% of the B, they would always end up at positive 52.5. Now, this is strange because this is not even the middle point. This is not even the halfway point of rotation between the two optical activities. So what I actually did is I made a little graph for you guys. You guys can really understand this. So notice that the Beta had a rotation of positive right? And the Alfa had a rotation of positive 1 12. Right? So that means at the very beginning, let's say that we started off with 100% of the beta Anna Marie. Well, that would give us 18.7 optical activity. But what was notices that after several days of it be sitting in an aqueous solution. The optical activity would get more and more and more positive until it reached this magical number of 52.5. Now, why? Why is that? And then the same thing happened with this guy with the Alfa. The Alfa would get lower and lower until it got to 52.5. Well, guys, the reason is because we learned, remember that we learned that specifically for a beta glucose. PIRA knows they the the beta prevails at a 64% equilibrium, and the Alfa prevails at a 36% equilibrium, meaning that if you were just start with one of them and allow it to mutual rotate. You're eventually gonna reach an equilibrium where 64% of the of the pirate dose is in the beta form and 36% is in the Alfa form. And that is why, at the end, the rotation that you end up getting is 52.5 because that happens to be right at the 64% mark off the difference between the two. What this shows is that 64% of it is the beta and Onley, 36% of it is the Alfa. If it had been 50 50 let's say that equally rated Thio exactly 50 50. Then we would expect a rotation right in the middle of these two, which is positive. 65. But we don't see positive 65. What we see is that it's a little bit more than 60. It's a little bit less than 65 which must mean that the one that's on that side is the majority. Because it's the one with lower optical activity. And when you actually do the numbers, it shows that 64% is equal to the beta. Okay, so anyway, this is proof that mutual rotation was occurring. Uh, you know, chemist, back in the day, they realized, Oh, this must mean that, um, this must mean that if I have an Alfa somehow it's going to equilibrium and become a beta. So then they started figuring out Well, what is a potential mechanism for this to take place? How could an Alfa potentially become a beta? Well, that's gonna be the next video. So hopefully this makes sense so far in terms of optical activity proving that mutual rotation exists. And in the next video, I want to go into the mechanism

Alright, guys. So while mutual rotation is possible in both acid and base, I'm on Lee going to show you the acid catalyzed mechanism. And that's because it turns out that the base catalyzed mechanism has a bunch of cross reactions that are that are possible that complicate the products. So usually this is just shown in acid. Okay, so let's go ahead and get started. The very first step is pro nation, as with any acid catalyzed mechanism. So I'm just going to redraw my hydro knee ums that I can have one accessible proton and the protein needed Oh, will be the O and the ring, because remember, we need to break this ring somehow. Okay, So what this is going to do is it's gonna give me a positively charged Oh, and at this point, I can use the electrons from my an America oxygen. Remember, that's the one we're trying to flip up and down to make a double bond. Okay, so two electrons from my oh can come down and make a double bond, and then I can break this bond in the ring to form an alcohol. So at this point, what's gonna happen is that the Cairo ality of this carbon is now lost because it turned into a double bond between tribunal plainer now it could It's right in between. It could be up or it could be down. Okay, also, this oh is gonna have a positive charge because it still has an h. Cool. Awesome. So now, guys, we're just going to start doing the reverse and get rid of that double bond. So this Oh, can now reform the rain kicking electrons back up. So this is going to do is it's gonna give me once again a positive Oh, and now I'm going to get the other Ohh! Now we're going to show that now it shifted to the up instead of down. And that's because this ohh could attack from either the top or the bottom so it could make the O h go up or could make it go down. In this case since we started from the down position, I'm trying to rotate it. Mewtwo rotated to the up positions. That's why I draw it up here and then finally, guys, all we have to do is deep Rotimi. So then deep rotates. We can regenerate that catalytic acid, and we're gonna go ahead and achieve a final product, which is now a beta de glue CO Pyrenees. Okay? And oh, I'm sorry Pira knows. And this is the process that turned. This is the middle rotation process that turns an outfit to a beta, and this is what's constantly taking place. And eventually they would reach an equilibrium based on the stability ease of each. We know that for glucose, it happens to be 64% of the beta. But if this was any other sugar, the number would be different and the animal might even be different. Maybe the Alfa would be favored with another sugar. Awesome, guys, great job. Let's move on.