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

Explanation

Glucose pentaacetate does not react with hydroxylamine. This shows the absence of aldehyde group in it. The cyclic structure of glucose contain -OH groups at C-1,C-2,C-3,C-4 and C-6. When treated with acetic anhydride, these five -OH groups get acetylated to form glucose pentaacetate.Since there is no free -OH group at C-1, it cannot change to the open chain form containing aldehyde group at C-1