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  • On the basis of which evidences D-glucose was assigned the following structure?

On the basis of which evidences D-glucose was assigned the following structure?


 

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1. Molecular formula : Molecular formula of glucose is has been found to be C_6H_{12}O_6

2. Straight chain sructure: 

(i) When aqueous solution of glucose is treated with sodium amalgam (Na/Hg) or sodium borohydride, it is reduced to sorbitol (or glucocitol) a hexahydric alcohol.

(ii) Prolonged heating with hydriodic acid and red phosphorous at 100^{\circ} C gives a mixture of n-hexane and 2-iodohexane.

The formation of n-hexane suggests that all the six carbon atoms in glucose are arranged in a straight chain structure of glucose.

3. Presence of five hydroxyl (-OH) groups: The formation of pentaacetate after acetylation with acetic anhydride indicated the presence of 5 -OH groups. As glucose is a stable compound the 5-OH groups are supposed to be present on different carbon atoms.

4. Presence of one primary alcoholic group: The oxidation reaction of glucose and gluconic acid with conc. Nitric acid yields the same dicarboxylic acid, saccharic acid or glucaric acid.

5. Presence of an aldehyde (-CHO) group: A tehrection of glucose with hydroxylamine is feasible it indicated the presence of carbonyl (CHOH)4 (>C = O) groups.
 

The above-mentioned observations, the open chain structure of glucose can be described as:

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