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

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Solution

$D-glucose reaction with N H_{2} O H$

In aqueous medium $D$ -glucose have open chain structure and free aldehydic group $- C H O$ is present here.

This $D$ -glucose then reacts with hydroxylamine $(N H_{2} O H)$ and produces oximes.

$Pentaacetate of D-glucose$

Pentaacetate of $D$ -glucose in aqueous medium does not form open chain structure and thus when it reacts with $N H_{2} O H$ , it does not form oxime indicating that there is absence of free aldehyde $(- C H O)$ group.

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