Question

Which of the following statement is not true for glucose?

• A. Glucose gives Schiff's test for aldehyde
• B. Glucose exists in two crystalline forms $\alpha$ and $\beta$
• C. Glucose reacts with hydroxylamine to form oxime
• D. The pentaacetate of glucose does not react with hydroxylamine to give oxime

Answer 1

The correct option is A Glucose gives Schiff's test for aldehyde

Glucose exists in two anomeric forms $\alpha$ and $\beta$ by mutarotation.


Aldehyde group react with hydroxylamine to give oxime.
Glucose with anomeric hydroxyl group can convert to ring opening structure which contain aldehyde.
Thus, it forms oxime with $N{H}_{2}OH$ and its pentaacetate does not react with $N{H}_{2}OH$ because its anomeric $OH$ group is converted into acetate group.

Pyranose structure (Closed ring) is quite stable and is not broken down by Schiff's reagent which is a weak base. Hence, it does not form hydrazone and giving a negative Schiff's test.

Hence, option (d) is correct answer.