Question

Which of the following statement is not true for glucose?

(JEE MAIN 2020)

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

Answer 1

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

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


Aldehyde group reacts with hydroxylamine to give oxime.
Glucose with anomeric hydroxyl group can convert to open structure which contains aldehyde group. Thus, it forms oxime with $N{H}_{2}OH$.
On the other hand, its pentaacetate does not have free aldehydic group so it does not react with $N{H}_{2}OH$.

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 give Schiff's test.

Hence, option (d) is correct answer.