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(1) Aldehydesgive 2, 4-DNP test, Schiff’s test, and react with NaHSO4 toform the hydrogen sulphite addition product. However, glucose does not undergothese reactions.
(2) Thepentaacetate of glucose does not react with hydroxylamine. This indicates thata free −CHO group is absent from glucose.
(3) Glucoseexists in two crystalline forms − ∝andβ. The ∝-form (m.p. = 419 K) crystallises from a concentratedsolution of glucose at 303 K and the β-form (m.p = 423 K) crystallises from ahot and saturated aqueous solution at 371 K. This behaviour cannot be explainedby the open chain structure of glucose.