Question

An example of non reducing sugar is:
A. Cane sugar
B. Fructose
C. Lactose
D. Glucose

Answer 1

Hint: The sugars which do not have a hydroxyl group attached to the anomeric carbon are called reducing sugars. When the sugar is in the open configuration, the alcohol group becomes a ketone or an aldehyde group.

Complete step by step answer:
Any sugar which can act as a reducing agent is known as a reducing sugar. It can act as a reducing agent due to the presence of a free aldehyde group or a free ketone group. All monosaccharides are reducing sugars along with some disaccharides, some oligosaccharides, and some polysaccharides.
The monosaccharides can be divided into two groups: the aldoses, which have an aldehyde group, and the ketoses, which have a ketone group. Ketoses must first tautomerize to aldoses before they can act as reducing sugars. Examples of monosaccharide reducing sugars are galactose, glucose, fructose, etc.
A disaccharide is formed from two monosaccharides. A disaccharide can be classified as a reducing sugar or a non – reducing sugar based on presence of a hydroxyl group at the anomeric carbon. If the hydroxyl group is present at the anomeric carbon, then the disaccharide is reducing, else it is a non – reducing sugar.

In the given question, sucrose is a non-reducing sugar due to the absence of hydroxyl group at the anomeric carbon. It is a dimer of glucose and fructose. It is also known as cane sugar. The structure of sucrose is:

Hence, the correct answer is (A) cane sugar.

Note: Remember that a ketose sugar first tautomerizes into an aldose sugar and then it is reduced. It can’t be oxidised in ketose form.