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Thursday, 16 March 2017

Bio molecule - II


6.Structure

(i) Fischer structure –

(+) Glucose has `D’ configuration as shown

' D’ means — OH group on first chiral `C’ from the bottom is on right hand and + means it is dextro rotator, i.e, it rotates plane polarized light towards right.

(ii) Cyclic Structure OF Glucose: the straight chain is unable to explain the following reactions.

(a) It does not give the 2, 4‐DNP test, Schiff’s Test and does not form the hydrogensulphide product with NaHSO3
(b) The pentacetate of glucose does not react with NH2OH, indicating the absence of free aldehydic group.

(iii) Glucose exist in 2 different crystalline forms α and β forms. These are called anomers. They differ in optical rotation, they also differ in melting point.

Anomers are isomers which have a different configuration across C‐1 (first chiral ‘C’ atom).

7. Glycosidic Linkage: The linkage between two monosaccharide units through oxygen is called the glycosidic linkage.

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