Mutarotation - Video Tutorials & Practice Problems
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concept
Mutarotation
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Video transcript
In this video, we're going to begin our discussion on mutarotation. Now, mutarotation is really just a specific type of epimerization, and so before we actually define mutarotation, it's first helpful to define epimerization. And so, epimerization is defined as the process of interconverting epimers. And really that's just a fancy way of saying changing one epimer into the other epimer. Now, of course, we know from our previous lesson videos that epimers are just specific types of diastereomers that differ only in the configuration of any one single chiral carbon. And so because epimerse are just specific types of diastereomers and diastereomers are not mirror images, this also means that epimers are not mirror images which is why this guy right here is kind of confused looking into the mirror and seeing that he is not looking at a mirror image. Now if we take a look at our image down below over here, notice that d glucose and d mannose are epimers. And the reason that they're epimers is because notice that they only differ from each other in the configuration of just one single chiral carbon carbon, and that is the c 2 chiral carbon that we have highlighted here. So notice that the c 2 chiral carbon on d glucose has a d configuration since it's pointing to the right. And notice that the c 2 chiral carbon on d mannose has an l configuration since it's pointed to the left. But outside of the configuration of the c 2 chirocarbon, they are identical to each other which is what makes these two epimers of each other. Now, the process of epimerization is literally the process of converting 1 epimer into the other epimer. And so, of course this is going to require changing the configuration. And so, if we have to change the configuration that means that we're going to have to break and reform bonds. And so, breaking and reforming stable covalent bonds is generally going to require a catalyst. And so, epimerization generally is going to require a catalyst such as an enzyme to break bonds and then reform the bonds in a different orientation. And again, this is all because there is a change in the configuration. And so moving forward, this line here requiring a catalyst is going to be something that we're going to want to keep in mind as we move on and discuss mutor rotation because mutor rotation will not require a catalyst. But here, this here concludes our introduction to epimerization and in our next lesson video, we'll talk about mutarotation. So, I'll see you guys there.
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concept
Mutarotation
Video duration:
5m
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Video transcript
So now that we've introduced epimerization, in this video, we're going to talk about mutorotation. And so as we already mentioned in our last lesson video, mutarotation is literally just a specific type of epimerization that's going to inter convert anomers instead of epimerse, and so this includes converting alpha anomers into beta anomers and vice versa And so if we take a look down below at our image, notice in the middle here, we have our open chain linear form of the sugar D glucose and we already know that the aldehyde group here on carbon number 1 can react with the alcohol group here on carbon number 5 and that will allow this linear monosaccharide to cyclize and form either this anomer over here on the left or this anomer over here on the right. And so notice that this anomer over here on the left has its alcohol group on the opposite side of the ring as the highest numbered carbon. So it's pointing down and towards the ants on the ground, so it's going to be the alpha anomer or alpha d glucopyrinose and then notice that this anomer over here has its hydroxyl group pointing upwards in the same direction as the highest numbered carbon. And so because the bumps of the betas are on the same side, this is going to be the beta anomer or beta D glucopyranose. And so mutarotation again is just gonna be the process of converting the alpha anomer to the beta anomer or vice versa. And so going from this anomer, over to this anomer over here is mutorotation. So, essentially, the pink arrow represents mutorotation. And also, going from this anomer, backwards to this anomer over here, this would also be mutarotation. Now, what's interesting to point out is that only the free anomeric carbons that are forming either a hemiacetal or hemiketal are actually able to muta rotate. And by free anomeric carbon, all we mean is that the anomeric carbon is part of either a hemiacetal or a hemiketal. And so we can see down below that this anomeric carbon is part of a hemiacetal. And so this is capable of mutor rotating and this one over here is also part of a hemiacetal. So, it's free to mute or rotate backwards as well. And so, what you'll notice is that one of the main differences between epimerization and mutarotation is that the process of mutarotation does not require a catalyst. So no catalyst is needed. And so it's true that mutorotation does require the breaking epimerization in epimerization in our last lesson video, the bonds that were being broken and reformed were very stable covalent bonds. And so, in order to break and reform stable covalent bonds, you're definitely going to need a catalyst. But here with mutorotation since hemiacetals and hemiketals are already relatively unstable, they do not need a catalyst in order to break apart and reform the linear monosaccharide which can then go on to close and form the opposite ring anomer. And so really this last line here describes what's happening with mutorotation, which is when one ring anomer briefly opens up. So, imagine this anomer opening up to this linear chain right here. And then, the linear chain can go and close again to produce the opposite ring anomer and that is the real process of mutorotation. And so because mutorotation does not require a catalyst, any sugar that has a free anomeric carbon is going to be mutarotating and solution and converting from 1 anomer into the other anomer. And so if there is a free anomeric carbon on the sugar, then we can expect to have a mixture of anomers in solution, a mixture of alpha and beta anomers. And so this here concludes our introduction to mutorotation and we'll be able to get some practice applying these concepts as we move forward. So I'll see you guys in our next video.
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Problem
Problem
Which of the following sugars undergoes mutarotation in neutral aqueous solution?