Chapter 7, Problem 1Q

Summary Introduction

To review:

The class of each of the given sugars.

Introduction:

Carbohydrates are the most abundant biomolecule present in the Earth. Based on the number of sugar units they are classified as monosaccharide, disaccharide, oligosaccharide, or polysaccharide. Monosaccharides are the simplest carbohydrate unit. They cannot be hydrolyzed further. When a monosaccharide contains an aldehyde as its functional group, it iscalledaldose. The presence of ketones as its functional group shows that it is ketoses.

Explanation of Solution

The simplest carbohydrate, monosaccharide can either be aldoses or ketoses based on its functional group. When the functional group is an aldehyde, it is called an aldose. It is a ketose when the functional group is a ketone. The class, to which the given molecules belong, is described below:

The above figure (a) is the structure of the monosaccharide l-Threose. l-Threose belongs to the aldose family. This sugar molecule has an aldehyde group in the terminal. Although there is ketone in its linear change, it is considered to be an aldotetrose.

The figure number (b) shows the structure of l-Xylulose. It has ketone as its functional group. l-Xylulose is a five-carbon monosaccharide. This is an example of ketopentose.

The above diagram (c) depicts the structure of l-Tagatose. This is an example of ketohexose as it contains a keto functional group and a six-carbon monosaccharide chain.

Conclusion

Thus, it can be concluded that the figure (a)depicts l-Threose, which is an aldotetrose. Figure(b) representsl-Xylulose, which is an example of ketopentose and figure(c) shows l-Tagatose, which is an example of ketohexose.