Question

Sucrose is not a reducing sugar since:
A.It is chemically stable.
B.It contains no free aldehyde or keto group adjacent to a >CHOH group.
C.It is built up of a fructose unit.
D.It is optically active.

Answer 1

Carbohydrates can be classified as reducing and non-reducing sugars. All those carbohydrates that can reduce Fehling’s solution and Tollens’ reagent are called reducing sugars. Because of the involvement of reducing groups of glucose and fructose in glycosidic bond formation, sucrose is a non-reducing sugar.

Complete answer:
Carbohydrates can be classified as reducing and non-reducing sugars. All those carbohydrates that can reduce Fehling’s solution and Tollens’ reagent are called reducing sugars.
A reducing sugar is any sugar that is capable of acting as a reducing agent. A sugar can act as a reducing agent if it has a free aldehyde group or free ketone group.Some examples of reducing sugars are monosaccharides galactose, glucose and fructose.
Sucrose has two monosaccharide units that are held together by a glycosidic linkage between C1 of alpha-glucose and C2 of beta-glucose. Since sucrose does not contain free aldehyde or free ketone groups adjacent to a >CHOH group.

Hence our answer is option B) It contains no free aldehyde or keto group adjacent to a >CHOH group.

Additional information:
Sucrose is a common sugar. We can find sucrose from plants.Sucrose is extracted and refined from either sugarcane or sugar beet. So that humans can use it. Sucrose is often used in some food recipes as a useful ingredient.
In the sugar refining process, raw sugar crystals are washed first and then they are dissolved into sugar syrup.

Note:
All monosaccharides whether aldose or ketose are reducing sugars. Since sucrose is disaccharide and also it does not contain free aldehyde or free keto group adjacent to >CHOH group, it can not act as reducing sugar.