Multiple Choice
Which of the following disaccharides are reducing sugars?
9. Carbohydrates
Reducing Sugars
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Which chemical group below indicates that the sugar is a reducing disaccharide? Is 'C' an acetal or ketal?
A
A
B
B
C
C
D
D
E
E
Verified step by step guidance1
Identify the reducing end of the disaccharide. A reducing sugar has a free anomeric carbon that can open to form an aldehyde group. In the image, look for a hemiacetal or hemiketal group, which is a carbon bonded to an -OH group and an -O- group.
Examine the structure at position 'E'. The presence of a free hydroxyl group on the anomeric carbon indicates that this is the reducing end of the sugar. This is because it can open to form an aldehyde group, making the sugar a reducing sugar.
Determine the nature of the linkage at position 'C'. An acetal linkage involves a carbon atom bonded to two -O- groups and no -OH group, while a ketal linkage involves a similar structure but originates from a ketone.
Analyze the structure at position 'C'. The carbon is bonded to two -O- groups and no -OH group, indicating that it is an acetal linkage. This is typical for the glycosidic bond in disaccharides.
Conclude that the sugar is a reducing disaccharide due to the free hydroxyl group at position 'E', and the linkage at 'C' is an acetal, not a ketal.
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