Q. 13.9 - An Introduction to General, Organic, and Biological Chemistry

Question

Classify each of the following monosaccharides as an aldopentose, ketopentose, aldohexose, or ketohexose:

a. Psicose is present in low amounts in foods. 

b. Lyxose is a component of bacterial glycolipids.

                         

Step-by-Step Solution

Answer

Part a) Hexos has a six-carbon chain, while ketose has a two-carbon chain. 

Part b) It is an aldopentose because it has a $5$-carbon chain and an aldehyde group.

Step 1: Introduction (Part a)

Monosaccharides are the construction blocks of disaccharides and polysaccharides. 

Step 2: Explanation(Part a)

• A ketone is a kettopentose. The carbonyl organization is on the second carbon atom in ketopentose $(C=O)$. A monosaccharide with five carbon atoms is known as pentose.
• A ketone is a ketohexose. The carbonyl organization is on the second carbon atom in ketohexose $(C=O)$. A monosaccharide with six carbon atoms is referred to as hexose.

Step 3: Psicose (Part a)

• Psicose's structure is shown below:

 

• The carbon chain psicose has six members. 
• On the second carbon atom$(C=O)$, the carbonyl group exists.
• The carbonyl group on the second carbon atom in ketohexose $(C=O)$is on the second carbon atom.
• Hexose refers to a six-carbon monosaccharide.
• As a result, psicose is ketohexose as a monosaccharide.

Step 4: Explanation (Part b)

• An aldehyde is an aldopentose. The carbonyl organization is on the primary carbon atom in aldopentose$(-CHO)$. A monosaccharide with five carbon atoms is known as pentose.
• An aldehyde is an aldohexose. The carbonyl organization is on the primary carbon atom in aldohexose$(-CHO)$. A monosaccharide with six carbon atoms is referred to as hexose.

Step 5: Lyxose (Part b)

• Lyxose's structure is shown below:

 

• The carbon chain lyxose has five members. 
• On the first carbon atom, the carbonyl group exists.
• The aldehyde is aldopentose. 
• The carbonyl group on the first carbon atom is present in aldopentose $(-CHO)$
• Pentose refers to a five-carbon monosaccharide.
• As a result, lyxose is an aldopentose monosaccharide.