Q. 13.10 - An Introduction to General, Organic, and Biological Chemistry

Question

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

a. A solution of xylose is given to test its absorption by the intestines. 

b. Tagatose, found in fruit, is similar in sweetness to sugar. 

                                 

Step-by-Step Solution

Answer

Part a) Xylose is an aldopentose since it has five carbons and an aldehyde group.

Part b) Tagatose is a ketohexose since it has six carbons and a keto group.

Step 1: Introduction (Part a)

Monosaccharides are the construction blocks of disaccharides and polysaccharides. 

Step 2: Explanation (Part a)

• 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 3: Xylose (Part a)

• Xylose's structure is shown below:

• Xylose is a carbon chain with five members. 
• On the first carbon atom, there is a carbonyl group $(-CHO)$.
• An aldehyde is an aldopentose. The carbonyl group is found on the first carbon atom in aldopentose $(-CHO)$. 
• Pentose is a five-carbon monosaccharide.
• As a result, aldopentose is the monosaccharide xylose.

Step 4: Explanation(Part b)

• 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 5: Tagatose(Part b)

• Tagatose's structure is shown below:

• Tagatose is a carbon chain that 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.
• Tagatose is a ketohexose monosaccharide.