Question

How do you explain the absence of aldehyde group in the pentaacetate of D-glucose?

Answer 1

D-glucose reacts with hydroxylamine (NH₂OH) to form an oxime because of the presence of aldehydic (−CHO) group or carbonyl carbon. This happens as the cyclic structure of glucose forms an open chain structure in an aqueous medium, which then reacts with NH₂OH to give an oxime.

But pentaacetate of D-glucose does not react with NH₂OH. This is because pentaacetate does not form an open chain structure.