Question:
The functional group(s) in reducing sugar that tests positive with Tollen’s reagent is (are)
The functional group(s) in reducing sugar that tests positive with Tollen’s reagent is (are)
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Only functional groups that can yield a free aldehyde in solution will give a positive Tollen’s test — typical of reducing sugars.
Updated On: Dec 5, 2025
- Aldehyde
- Ketone
- Hemi-acetal
- Acetal
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The Correct Option is A, B, C
Solution and Explanation
Step 1: Recall what Tollen’s reagent detects.
Tollen’s reagent is an ammoniacal solution of silver nitrate that oxidizes aldehydes (–CHO) to carboxylates while reducing Ag$^+$ to metallic silver (silver mirror test).
Step 2: Relation to reducing sugars.
- Reducing sugars (like glucose) contain a free aldehyde or a hemiacetal group that can open up to form an aldehyde in solution.
- Ketones (like in fructose) do not directly react unless tautomerization produces an aldehyde form.
- Acetals are stable and do not react with Tollen’s reagent.
Step 3: Conclusion.
Reducing sugars test positive due to the presence of aldehyde or hemiacetal groups.
Tollen’s reagent is an ammoniacal solution of silver nitrate that oxidizes aldehydes (–CHO) to carboxylates while reducing Ag$^+$ to metallic silver (silver mirror test).
Step 2: Relation to reducing sugars.
- Reducing sugars (like glucose) contain a free aldehyde or a hemiacetal group that can open up to form an aldehyde in solution.
- Ketones (like in fructose) do not directly react unless tautomerization produces an aldehyde form.
- Acetals are stable and do not react with Tollen’s reagent.
Step 3: Conclusion.
Reducing sugars test positive due to the presence of aldehyde or hemiacetal groups.
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