SME
Organic Chemistry II · Problem type
Reducing or nonreducing sugar?
Use this for “Is maltose a reducing sugar? Will it give a silver mirror with Tollens’ reagent?”
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Does the sugar still have a free anomeric carbon?
Tap a card, then tap its group.
Find each ring’s anomeric carbon, the one bonded to two oxygens. Is one of them still an OH, not a link?
Assumptions
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A reducing sugar has a free anomeric carbon, a hemiacetal or hemiketal, that opens to the open chain and is oxidized by Tollens’ or Benedict’s reagent.
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Fructose is a ketose, yet it reduces too: in base it turns into an aldose through its enediol.
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A glycoside, with OR in place of the anomeric OH, is an acetal: it stays closed in base and does not reduce.
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