Reducing vs. nonreducing sugars
Which sugar gives a negative result with Benedict's reagent?
Answer D: explanation for every choice
A
Glucose has a free anomeric carbon, so its open-chain aldehyde reduces Cu²⁺.
B
Fructose is a ketose, but it tautomerizes to an aldose under the basic test conditions, so it is a reducing sugar.
C
Maltose has one glucose with a free anomeric carbon, so it is reducing.
D
Correct. Sucrose's glycosidic bond joins the anomeric carbons of both glucose and fructose (α1→β2), so neither is free.
TakeawayA sugar is reducing if it has a free anomeric carbon (a hemiacetal or hemiketal).
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb14.