Question

4. Simple sugars still behave as reducing sugars when they form this structure: a) Acetal b) Ketal c) Hemi-acetal d) Both acetal and ketal (please explain your answer!!)

Answer 1

4. Simple sugars behave as reducing sugars when they form : c) Hemiacetal

In a hemiacetal form the sugars are in protected form of aldehydes. This opens up during the reaction and behaves as reducing sugars, itself getting oxidized during the process of redox reaction. For example aldoses form cyclic hemiacetals which when opened act as reducing agents. It is a mandatory requirement for sugars to have an aldehyde to act as reducing sugars. Ketoses which can tautomerise to an aldehyde also acts as reducing sugars.