Question

From the given following (A to D) cyclic structures, those which will not react with Tollen's reagent are : 

• A. A and D
• B. B and C
• C. A and B
• D. B and D

Hint:

Check the anomeric carbon (the one bonded to two oxygens). If it has an -OH group (hemiacetal), it's a "reducing" sugar and will react with Tollen's.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Tollen's reagent ($[Ag(NH_3)_2]OH$) is used to detect aldehydes. In cyclic carbohydrates or similar structures, only hemiacetals can open up into an aldehyde form to give a positive Tollen's test. Acetals (where the anomeric carbon is bonded to two -OR groups) are stable in basic conditions and will not react.

Step 2: Detailed Explanation:
- Structures A and C typically represent hemiacetals (reducing sugars) which exist in equilibrium with their open-chain aldehyde forms. They react with Tollen's reagent.
- Structures B and D represent acetals or glycosides (non-reducing sugars) where the -OH group on the anomeric carbon has been replaced by an -OR group. Because they cannot revert to an open-chain aldehyde in the basic medium of Tollen's reagent, they will not react.
Step 3: Final Answer:
The structures that will not react are B and D.