Question

Which one of the following is an example of non reducing sugar?
(A) Sucrose
(B) Lactose
(C) Maltose
(D) Cellobiose

Answer 1

Hint: You should know that a non reducing sugar is any sugar that is not capable of acting as a reducing agent because it has no free aldehyde group or free ketone group. Now try to recall functional groups present in the above options to reach the correct answer.

Complete step by step answer:
> Non reducing sugars - A non-reducing sugar has no free carbonyl groups. They are in acetal or ketal form. These sugars do not show mutarotation.
Common examples for these are Sucrose, raffinose, gentianose and all polysaccharides.
> Reducing sugars - A non-reducing sugar has free carbonyl groups. They are in hemi-acetal or hemi-ketal form. These sugars show mutarotation.
Common examples for these are all monosaccharides and some disaccharides (Maltose, lactose and cellobiose)
> Sucrose is not a reducing sugar because it lacks the ability to form either aldehyde or a ketone in a basic solution. Reducing capability is defined by the presence of free or potential aldehyde or ketone groups.
Therefore, the correct answer is option A.

Note:
> As we know Disaccharides consist of two monosaccharides and may be either reducing or nonreducing. Even a reducing disaccharide will only have one reducing end, as disaccharides are held together by glycosidic bonds, which consist of at least one anomeric carbon. With one anomeric carbon unable to convert to the open-chain form, only the free anomeric carbon is available to reduce another compound, and it is called the reducing end of the disaccharide.
> A nonreducing disaccharide is that which has both anomeric carbons tied up in the glycosidic bond.Similarly, most polysaccharides have only one reducing end.