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Write three such behaviours of glucose which cannot be explained by an open chain structure of glucose molecule. What alternative structure has been proposed for the glucose molecule? |
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Answer» The following reactions cannot be explained by the open chain structure of glucose. (i) Despite having the aldehyde group, glucose does not give 2, 4– DNP test, Schiffs test and it does not form the hydrogensulphite addition product with NaHSO3 . (ii) The penta acetate of glucose does not react with hydroxyl amine indicating the absence of free —CHO group. (iii) D–Glucose on treatment of methyl alcohol in the presence of dry HCl gas gives two isomeric nonomethyl derivatives known as α-D-glucoside and methyl β– D–glucoside. These glucosides do not reduce fehling solution and also do not react with hydrogen cyanide indicating the absence of free —CHO group. A ring structure called pyranose structure (α- or β-) is proposed for the glucose molecule. |
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