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Expalinaboutthe cyclis structure of Glucose . |
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Answer» Solution :(i) Fischer identifiedthat theopenchain Penta hydroxyl adhehydestrcuture of glucosethat theproposed did notcompletelyexplainits chemicalbehaviour. (ii)Unlikesimplealdehyde , glucose did not formcrystallinebisulphate compound with sodiumbisulphate. Glucose does notnot give Schiff.s TESTAND penta ACETATE derivativeof glucose wasnot oxidisedby Tollen.s reagent. Thisbehaviourcouldnot beexplainedby openchain structure. (iii)  (iv) In order to explain these is was proposed that one of thehydroxyl groupreacts withaldehydegroupto forma cyclic structure(hemiacetal form). This alsoresultsin the conversationof theachiral aldehydecarbon into a chiralone leadingthe possibilityof twoisomers. Thesetowisomersdiffer onlyin theconfigurationof `C_(1)` carbon. Theseisomersare calledanomers. (V) The twoanomericformsof glucoseare called- and `beta` - forms. Thiscyclic structure ofglucoseis similarto pyran, a cyclic compound with 5 carbon and oneoxygenatom, and henceis calledpyranoseform. (vi) The specificrotation of pure`alpha` - and `beta`- (D) glucoseare `112^(@) & 18.7^(@)` respectively. HOWEVER , whenpure form any one of thesesugars dissolved in water slowinterconversion of- D glucoseand `beta` - Dglucose via open chain form until equilibrium is estabishedgivingconstatn specific rotation `+53^(@)` . Thisphenomenone is calledmutarotation. |
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