Question

Statement I: The structure of Maltose is given below: Maltose is a non-reducing sugar.

Statement II: The structure of Lactose is given below: Lactose is a reducing sugar.

In the light of the above statements, choose the correct answer:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Before deciding if a disaccharide is reducing, work out which carbon numbers the glycosidic bond actually joins in each sugar. If the bond leaves even one anomeric carbon free on either unit, the sugar can still open into an aldehyde form and act as a reducing sugar.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A sugar is "reducing" if it has a free hemiacetal group (an anomeric carbon not involved in a glycosidic bond). This allows the ring to open into an aldehyde form that can reduce Tollen's or Fehling's reagents.

Step 2: Key Formula or Approach:
1. Maltose: Glucose + Glucose ($\alpha$-1,4 bond). 2. Lactose: Galactose + Glucose ($\beta$-1,4 bond). 3. Sucrose: Glucose + Fructose (1,2 bond).

Step 3: Detailed Explanation:
1. Maltose analysis: In maltose, the C1 of the first glucose is bonded to the C4 of the second glucose. The C1 of the second glucose is free. Therefore, maltose is a reducing sugar. Statement I is false. 2. Lactose analysis: In lactose, the C1 of galactose is bonded to the C4 of glucose. The C1 of the glucose unit is free. Therefore, lactose is a reducing sugar. Statement II is true.

Step 4: Final Answer:
Statement I is false, but Statement II is true.