Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.

Open structure of D-glucose could not explain the following reactions:

(i) Despite having the aldehyde group, glucose does not give 2,4 DNP test and Schiff’s test.

(ii) Glucose does not react with sodium hydrogen sulphite to form addition product.

(iii) The absence of free –CHO group is shown when the penta-acetate of glucose does not react with hydroxyl amine.

(iv) When glucose is heated with methanol in the presence of dry HCl gas, it forms two isomeric monomethyl derivatives known as α-D-glucoside and β-D-glucoside. Since only one molecule of methanol is used for the formation of methyl glucosided, these must be hemiacetals.