Question

Consider the following statements regarding carbohydrates: Assertion (A): Sucrose is a non-reducing sugar. Reason (R): In sucrose, both the anomeric carbon atoms of glucose and fructose participate in glycosidic bond formation. Choose the correct option.

• A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• C. Assertion is true, but Reason is false
• D. Assertion is false, but Reason is true

Hint:

Quick NCERT Revision: Reducing Sugars: \[ \text{Glucose, Maltose, Lactose} \] Non-Reducing Sugar: \[ \text{Sucrose} \] Reason: Both anomeric carbons participate in glycosidic bond formation, leaving no free reducing end.

Answer 1

The Correct Option is A

Concept: Biomolecules is one of the highest-weightage chapters in recent CUET Chemistry papers. Questions are frequently asked from:
• Reducing and non-reducing sugars
• Glycosidic linkage
• Mutarotation
• Structure of sucrose
• Structure of cellulose and starch This question specifically tests the structural reason behind the non-reducing nature of sucrose.

Step 1: Understand what makes a sugar reducing. A carbohydrate behaves as a reducing sugar when it possesses a free: \[ \text{Anomeric carbon} \] that can open to form an aldehyde or ketone group. Examples: \[ \text{Glucose} \] \[ \text{Maltose} \] \[ \text{Lactose} \] These sugars can reduce: \[ Ag^+ \] (Tollen's reagent) or \[ Cu^{2+} \] (Fehling's solution).

Step 2: Recall the structure of sucrose. Sucrose consists of: \[ \alpha\text{-D-Glucose} \] and \[ \beta\text{-D-Fructose} \] joined through a glycosidic linkage. The linkage is: \[ \alpha(1\rightarrow2)\beta \] This means:
• Carbon-1 of glucose participates.
• Carbon-2 of fructose participates. Both of these carbons are anomeric carbons.

Step 3: Determine whether any free anomeric carbon remains. Since both anomeric carbons are involved in bond formation: \[ \boxed{\text{No free anomeric carbon remains}} \] Therefore sucrose cannot open into a free aldehyde or ketone form. Hence: \[ \boxed{\text{Sucrose is non-reducing}} \]

Step 4: Evaluate the Assertion. Assertion: Sucrose is a non-reducing sugar. This statement is correct. \[ \boxed{\text{Assertion = True}} \]

Step 5: Evaluate the Reason. Reason: Both anomeric carbon atoms participate in glycosidic bond formation. This statement is also correct. \[ \boxed{\text{Reason = True}} \]

Step 6: Check whether the Reason explains the Assertion. Because both anomeric carbons are involved: \[ \text{No free reducing end exists} \] Therefore sucrose cannot behave as a reducing sugar. Thus the Reason directly explains the Assertion. \[ \boxed{\text{Reason correctly explains Assertion}} \]

Step 7: Final conclusion. Both statements are true and the Reason correctly explains the Assertion. Hence: \[ \boxed{\text{Option (A)}} \]