Fructose can also act as a reducing sugar, even though it has a ketone group instead of an aldehyde group. Under basic conditions, the fructose molecules can, essentially, have the location of the carbonyl bond switched to convert them into a glucose molecule. This occurs in a number of steps involving removing hydrogens from the #1-C and its oxygen and moving them to the #2-C and its oxygen.
Your experiment for this week's lesson is to test a variety of carbohydrates to see whether or not they are reducing sugars. In a sense, that test can be used to determine the presence of a monosaccharide because a monosaccharide is a reducing sugar and, therefore, presumably, if you have a reducing sugar, you have a monosaccharide. But for reasons that you will see soon, that presumption is not entirely correct. If you wish, you could do the experiment at this time, although I would recommend that you wait until after we've talked about disaccharides and polysaccharides.
E-mail instructor: Sue Eggling
Clackamas Community College