Reducing sugars?

[freedyx3]

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Anyone have an idea how do you ID a reducing sugar. And what is the diff between a reducing sugar and nonreducing sugar.

Thanks

 

[rcmonkeypie]

reducing sugars are those that can be oxidized. Remember, in any redox reaction, there is always a species that gets oxidized and another that can be reduced. Identify the anomeric carbon first. If it's a hemiacetal it is a reducing sugar because it can be oxidized. For example, glucose is a reducing sugar. It exists as a cyclic hemiacetal and can be oxidized to a lactone (cyclic ester). Sucrose on the other hand is a NON-reducing sugar.
Here's the rule: you MUST have a hydroxy group (OH) attached to the anomeric carbon. As long as it's NOT a tertiary alcohol, it can be oxidized and is thus considered a reducing sugar. In general, aldoses are reducing sugars and ketoses are NOT. hope this helps.

 

[PDPjester]

really? i read that ketose is oxidized when mixed with Tollens reagent, and whatever sugar that reacts with it is a reducing sugar. Thus, assumed it too is.

 

[rcmonkeypie]

jester is correct. both aldoses AND ketoses are reducing sugars, technically speaking. However, in lab, this is often not the case (i was relying on my own experience... sorry). But everything else regarding my original reply was correct.

 

[PDPjester]

monkeypie, that is interesting. All that we learn in text book is not always the case in real life. life is funny that way, isn't it?