Glucose and fructose are reducing
sugars as they reduce Fehling's solution and Tollen's reagent. In aqueous
solution these saccharides containing hemiacetal or hemiketals exist in equilibrium with a small amount of open
chain aIdehyde or alpha-hydroxy
ketonic form. When
treated with the above said reagents the open chain form is oxidised. As the
open chain form is consumed with some reagent, the equilibrium gets disturbed
and more of open chain aldehyde or alpha-hydroxy ketone is formed and thus reduction of these reagents
keeps on going. On the other hand sucrose is a non reducing sugar because it
does not reduce these reagents. This is due to the reason that the reducing
groups present in the constituting monosaccharide units are not free and are
involved in the formation of glycosidic linkages.
Related Questions:
