Amongst the aldopentoses shown below, identify the pairs that ...

Question

Amongst the aldopentoses shown below, identify the pairs that are enantiomers.

Structures of six aldopentoses for identifying enantiomer pairs in biochemistry.

____ and ____

Accepted Answer

So this practice problem says, amongst the aldopentoses shown below right here, identify the pairs that are enantiomers. And recall that enantiomers are non superimposable mirror images. And so if we start with sugar number 1 over here, if we want to find the enantiomer, all we have to do is find the mirror image. And so, one way to help us find the mirror image is to note that for all of these chiral carbons right here, the Oh groups are pointing to the right. And so if we wanna find the mirror image, we need to find, the structure where all of the Oh groups are pointing in the opposite direction. So all of the Oh groups pointing to the left instead of pointing to the right. And notice that matches with sugar 6. Notice that all of the hydroxyl groups are pointing to the left instead of pointing to the right, which means that sugar 1 and sugar 6 are pairs of enantiomers. So over here on the left hand side, we can say that sugar 1 and sugar 6 are indeed pairs of enantiomers. Now recall that enantiomers is a word that describes the relationship only between 2 sugars. And so what that means is that sugar 1 and sugar 6 are not gonna be possible answers, are not gonna be pairs of enantiomers with anything except each other. And so as we move on to sugar 2, we know that sugar 2, is not going to be a pair of enantiomers with sugar 1 or sugar 6. And so taking a look at sugar 2, we can apply this same strategy where we look at the chiral carbons and we look at the hydroxyl groups coming off. And so you can see that the c 2 hydroxyl is going to the right and the c 3 and c 4 hydroxyls are going to the left. And so if we wanna find the enantiomer of sugar 2, then all we need to do is find these hydroxyls that are going in the opposite directions. And notice that matches with sugar 4. So notice that it's C2 hydroxyl is going left in the opposite direction and it's c 3 and c 4 hydroxyls are going to the right in the opposite directions. And so sugar 2 and sugar 4 are indeed pairs of enantiomers and for that reason, we can go ahead and list them over here. Sugar 2 and sugar 4 are pairs of enantiomers and again, enantiomers is a word that describes the relationship between just 2 sugars. So what that means is that sugar 2 and sugar 4 are enantiomers with each other, but they're not going to be enantiomers with any of the other sugars on here. So we can go and cross those off. And so, of course, what we're left with is just sugar 3 and sugar 5. So that means that they're going to be enantiomers with each other. Right? Sugar 3 and sugar 5? No. Not quite. So if we take a closer look and apply the same strategy to sugar 3, notice that it's c 2 and c 3 hydroxyls are pointing to the right, and then c 4 hydroxyls pointing to the left. And so if we wanted to find the enantiomer of sugar 3 then these hydroxyls need to be pointing in the opposite directions. However, when we take a look at sugar 5 over here, notice that its first hydroxyl is pointing in the same direction. So it's not pointing in the opposite direction like it should. And, the Oh here is pointing in the opposite direction, and so is this one down below but the first one is not and that means that sugar 3 and sugar 5 are not enantiomers of each other And so really this last blank here is just a trick and we can cross it off. And so the answers to our practice problem are sugar 16 and sugar 24 are enantiomers of each other. And that concludes this practice problem, so I'll see you guys in our next video.

Struggling with Biochemistry?

Amongst the aldopentoses shown below, identify the pairs that are enantiomers.

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Stereochemistry of Monosaccharides practice set

Struggling with Biochemistry?

Amongst the aldopentoses shown below, identify the pairs that are enantiomers.____ and ________ and ________ and ________ and ____

Watch next

Stereochemistry of Monosaccharides practice set

Amongst the aldopentoses shown below, identify the pairs that are enantiomers.

and
and
and
and