Question

Which of the following sugars are reducing sugars? Why?

Answer 1

b is a reducing sugar as its oxygen from carbonyl carbon is not attached to any other structure

Look at the carbons on either side of the oxygen. One will be attached to a CH2OH group. Do not

focus on that one. The carbon on the other side is the anomeric carbon. that free oxygen is present in sugar b and not the rest one so a, c, and d are non reducing.A reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group. All monosaccharides are reducing sugars, along with some disaccharides, oligosaccharides, and polysaccharides.A reducing sugar is easily oxidized. What makes it easy to oxidize is an "oxo" group, either an aldehyde or a ketone.Glucose and maltose have an aldehyde group and fructose will have a ketone group. The open-chain form of the sugar is what can be oxidized and is, therefore a reducing sugar (that is, it reduces something else, often silver or copper cations to silver or copper metal- used in analysis). If the anomeric carbon is blocked (i.e., instead of -OH it is -OCH3 or -O-sugar or -O-almost-anything) the sugar cannot open up and the sugar is non-reducing. If the hydroxyl is there, then it is a reducing sugar.