In the table below, indicate what the result of a Fehling's, B...

Question

In the table below, indicate what the result of a Fehling's, Benedict's, and Tollen's test would be for each of the two sugars and what conclusion can be made about the properties of the sugars.

Table showing sugar molecules and results of Fehling's, Benedict's, and Tollen's tests.

Accepted Answer

So this practice problem says, in the table below shown right here, indicate what the result of a failings, benedict's, and talons test would be for each of the 2 sugars shown here and here and what conclusion can be made about the properties of these 2 sugars And so, of course, we know from our previous lesson videos that the failings, Benedict's, and Talens test are all color change experiments that are testing for the presence of reducing sugars. And so in the presence of a reducing sugar, we expect to see a color change. And so what we wanna do is take a look at these 2 sugar molecules and determine if they are reducing sugars. And of course, when it comes to cyclic monosaccharides like these 2 sugars here, we need to determine if the, anomeric carbon is part of either a hemiacetal, hemiketal, acetal, or ketal. And so when we take a look at the anomeric carbon of this sugar right here, notice it's right here and recall that the anomeric carbon is the only carbon atom that's bonded to 2 oxygen atoms. And so notice that this anomeric carbon is part of a hemiacetal. So this is a hemiacetal and so we know that it's a hemiacetal because notice that it only has 1 OR group. It has a free hydroxyl group and, of course, going down, it still has its hydrogen. And so, of course, hemiacetals are going to be susceptible to breaking apart into its linear form and generating an aldehyde group. And the aldehyde group is capable of being oxidized. And once it's, oxidized, of course, it's going to create a color change. And so with the failings and Benedict's test, we would expect there to be a color change. So we would expect the color, to change. And of course, we would expect to end up getting a red, precip a red color, upon, the result. And so we would actually expect a very similar result for the Benedict's test and so we could put that in here as well. And then for the talents test, we would also expect a color change, but this time instead of getting a red color, we would expect to get a silver mirror. And then the final conclusion here is that this is a reducing sugar because of the color changes and, because of the presence of the hemiacetal. Now, when we take a look at this sugar over here and we try to look for its anomeric carbon, notice that it actually does not have an anomeric carbon because recall that the anomeric carbon is the only carbon atom bonded to 2 oxygen atoms. But if you take a look at all of these carbon atoms, notice that none of them are bonded to 2 oxygen atoms directly. And so what this means is that there is no hemiacetal or hemiketal. And that means that this ring right here is not capable of opening up and generating a free aldehyde group. And of course, that means that we would expect to get no color change. And so if there's no color change, then of course, it's going to remain a blue color. So, we can put in blue color here and we would expect to get a very similar result for the Benedict's test. And then, of course, for the talents test, there would also be no color change, but instead of being a blue color, it would just be clear and it would not be silver. And so, of course, this is an indication that this sugar right here is not a reducing sugar. Instead, this is going to be a non a non reducing sugar. And so relatively easy easy practice problem And so the main idea again is to be able to look at sugars and identify if they have hemiacetals or hem Ketals and, determine if they are reducing or non reducing. And so that concludes this practice problem and I'll see you guys in our next video.

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In the table below, indicate what the result of a Fehling's, Benedict's, and Tollen's test would be for each of the two sugars and what conclusion can be made about the properties of the sugars.

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