Which of the following statement is not true for glucose? [JEE Main 2020, 8 Jan (Shift 1)]
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Which of the following statement is not true for glucose? [JEE Main 2020, 8 Jan (Shift 1)]
✓ Correct answer: b) Glucose gives Schiff's test for aldehyde
ExplanationThe statement that is not true for glucose is that glucose gives Schiff's test for aldehyde.Here is an analysis of each statement: A. Glucose exists in two crystalline forms α and β: This statement is true.Glucose forms cyclic hemiacetal structures and can exist in two anomeric forms, α-D-glucopyranose and β-D- glucopyranose.B. Glucose gives Schiff's test for aldehyde: This statement is not true (false).Although glucose has an aldehyde group in its open-chain structure, in an aqueous solution, it predominantly exists in a stable cyclic (pyranose) form where the aldehyde group is involved in a hemiacetal linkage and is not free to react with Schiff's reagent.Thus, it gives a negative Schiff's test.C. Glucose reacts with hydroxylamine to form oxime: This statement is true.Because the cyclic form of glucose can exist in equilibrium with a small amount of the open-chain form, it can still undergo some reactions characteristic of aldehydes, such as reacting with hydroxylamine (NH2O ) to form an oxime.D. The pentaacetate of glucose does not react with hydroxylamine to give oxime: This statement is also true.In glucose pentaacetate, the aldehyde group is protected by acetylation, and all hydroxyl groups are also acetylated.This prevents the formation of the open-chain structure required to react with hydroxylamine to form an oxime.
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