Chapter 25: Carbohydrates
Sugars that contain aldehyde groups that are oxidised to carboxylic acids are classified as
Common test reagents are :
Benedicts reagent (CuSO
Fehlings reagent (CuSO
They are classified as
which forms as a red precipitate, copper (I) oxide.
Remember that aldehydes (and hence aldoses) are readily oxidised (
In order for oxidation to occur, the cyclic form must first ring-open to give the
So any sugar that contains a
will be a reducing sugar.
But glycosides which are acetals are not reducing sugars.
=> reducing sugar
=> non-reducing sugar
Ketoses can also be reducing sugars because they can isomerise (a
) to aldoses via an enediol:
Dr. Ian Hunt
, Department of Chemistry, University of Calgary