Select the appropriate label for each of the three following m...

Question

Select the appropriate label for each of the three following monosaccharides:

Accepted Answer

Alright. So this practice problem wants us to select the appropriate label for each of the 3 following monosaccharides, arabinose, threose, and erythralose. And so we're gonna start with arabinose over here on the far left. And so first, we're going to classify arabinose based on the nature of its carbonyl group, which recall a carbonyl group is just a carbon double bonded to an oxygen. However, when I take a look at this arabinose molecule here, I don't see any carbon atoms that are double bonded to anything. And so that's when we need to realize that this c h o group that we have here is a condensed form of an aldehyde group, a condensed form of a carbonyl group. And so this is an aldehyde group because it's at the very end of the molecule, which means that we can eliminate any answer options that suggest this might be a keto group. So that means that we can eliminate option b and we can eliminate option d. So next, we need to count up the number of carbon atoms that there are. So we have 1, 2, 3, 4, 5 carbon atoms, which suggest that this is going to be a pentose. And so, we can eliminate option c here, which suggests that it is a tetrose. It would be a tetrose if it had 4 carbon atoms. And so the correct answer here is actually going to be option a. This is an aldopentose. An aldo because it has an aldehyde group and a pentose because it has five carbons. So we can indicate that a is the correct answer for part a. So now moving on to part b, threose, what we can see is that there is another aldehyde group here at the end. And so it's going to be an aldose, not a ketose. So we can eliminate any answer options that suggest it's a ketose, such as option a and option d. And then when we count the number of carbons, we can see there are 1, 2, 3, 4 carbon atoms. So this time, it's going to be a tetrose because it has 4 carbon atoms. And we can eliminate the pentose option since that would be again if it had 5 carbon atoms. So we can indicate that the correct answer for threose is that it is a aldotetros. So then moving on to our final option here, erythralose, what we can see is that its carbinal group is right here in the middle, and this is a ketone group because it has an r group, 2 r groups branching off. And so because this is a ketone, it's going to be a ketose and we can go ahead and eliminate any answer option that suggest that it is an Aldose such as option a and option c. And then counting the number of carbons, we can see there are 1, 2, 3, 4 carbon atoms making this a tetrose. And so, of course, we can go ahead and indicate that option d, keto tetrose is correct. Ketopentose would be again if it had 5 carbon atoms, but that's not the case here. So then we can say that erythralose is indeed a keto tetrose. And so that concludes this practice problem and I'll see you guys in our next video.

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Select the appropriate label for each of the three following monosaccharides:

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Monosaccharides practice set