Why does glucose, despite having an aldehyde group, not give Schiff’s test and fail to form a hydrogensulphite addition product with NaHSO₃?

Glucose, despite having an aldehyde group, does not react with Schiff’s reagent or form a hydrogensulphite addition product with NaHSO₃ due to its intramolecular hemiacetal formation. In aqueous solution, glucose undergoes an intramolecular reaction between the aldehyde group and one of the hydroxyl groups, forming a stable cyclic hemiacetal. This intramolecular hemiacetalization prevents the aldehyde group from being available for reactions with Schiff’s reagent or NaHSO₃. The aldehyde group is effectively masked within the stable cyclic structure, rendering glucose unreactive toward these reagents designed for aldehyde detection or reaction.