Question

Classify the following monosaccharides:

Short answer

D-ribose is an aldopentose

D-sedoheptulose is a ketoheptose

D-mannose is an aldohexose

Step-by-step solution

Monosaccharides

Monosaccharides are building blocks of complex carbohydrates. Monosaccharides contain only a single unit and cannot be further hydrolyzed.

Monosaccharides are also called simple sugars and are polyhydroxy compounds.

Monosaccharides react with each other to form disaccharides and polysaccharides. The reaction between two monosaccharides is a dehydration reaction removing a molecule of water. They are linked by ether bonds called glycosidic linkages.

Classification of monosachharides

The main categorization of monosaccharides is based on the number of carbon atoms and the functional group in them. The carbon atoms in a monosaccharide typically range from 3 to 8 and are named trioses, tetroses, pentoses, etc.

The functional group in a monosaccharide can be an aldehyde or a ketone. Aldoses contain the aldehyde group at the end carbon, and ketoses have the ketone group at the second carbon.

The class of a monosaccharide is represented by the number of carbon atoms and the functional group.

Classification of the given sugars

The classification of sugars can be done by identifying their functional group and counting the number of carbon atoms in it.

D-ribose contains five carbons and therefore is a pentose. The functional group in D-ribose is an aldehyde group, and it is an aldose. Therefore, D-ribose is an aldopentose.

D-sedoheptulose contains seven carbon atoms and is a heptose. The ketone group at the second position makes it a ketose. Therefore, D-sedoheptulose is a ketoheptose.

D-mannose is a hexose as it contains six carbon atoms. The end carbon is an aldehyde making it an aldose. Therefore, D-mannose is an aldohexose.