I did a lab experiment where we used 7 test tubes all with different types of su

Question

I did a lab experiment where we used 7 test tubes all with different types of sugars. I came to the conclusion that all were reducing sugars except sucrose and mannose, as the mannose gave me a blue color in the Benedicts test. I can find where I am correct with the sucrose, but is mannose considered a reducing or a non-reducing sugar? Did my test turn out wrong?

Explanation / Answer

Mannose is a reducing sugar. It has one CHO group. An Aldehydic group can be oxidised to acid. Mannose has an aldehydic group which can get oxidised. At the same time it can reduce other substances/molecules. So mannose is a reducing sugar. i.e. it can reduce other molecules. RCHO +[O] --------> RCOOH Only sugars which have free aldehydic group (CHO) can reduce others. Sugars containing ketonic group are not reducing sugars. Mannose happens to be an epimer of Glucose which means both molecules differ in the configuration of one carbon atom. In mannose one hydroxyl group at carbon-2(C2) is oriented differently from that of glucose. It seems that there was something wrong in your experiment.

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