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Explain the structure of Fructose |
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Answer» Solution :Structure of fructose :Fructose is thesweetest of all known sugars. It isreadily solublein water. Freshsolution of fructosehas a specificrotation -` 133^(@)`which changesto `- 90^(@)`at equilibriumdue to mutarotation . SIMILAR to glucose , the structureof fructoseis deducedfromthe followingfacts. (i) Elementalanalysisand molecularweight determination of fructoseshow that it hasthe molecularformula ` C_(6)H_(12)O_(6)` (ii) Fructoseor redcutionwith HI and redphosphorusgivesa mixtureof n- hexane(major product) and 2 - iodohexane ( minor product). Thisreactionindicatesthat the sixcarbonatomsin fructose are ina straight chain. ` " Fructose " overset(" HI/P") underset(" Reducation")to CH_(3) - CH_(2) - ._(4) CH_(3) + CH_(3) -underset(|)CH ( CH_(2))._(3) CH_(3)` (iii)Fructosereactswith ` NH_(2)OH and HCN`. it shows the presenceof carbonyl groups in the moleculeof fructose. (iv) Fructosereacts withaceticanhydridein thepresence of pyridineto formpentaacetate . Thisreaction indicates the presence of fivehydroxylgroups in a fructose molecule. (v)Fructose is notoxidized by brominewater . This rulesout the possbility of presenceof an ALDEHYDE (-CHO) group. (vi) Partial reduction of fructose withsodiumamalgam and water produces mixturesof sorbitoland manitol whichare epimersat secondcarbon. New asymmetric carbon is formedat C-2. Thisconfirms the presence of keto group  (vii) On oxidation whichnitricacid,it givesglycolic acidand tartaric acidswhichcontainsmallernumberof carbonatomsthan in fructose.  This shows that a ketogroupis present in C-2. It ALSO shows the presence of 10 alcoholicgroups at C-1 and C-6. ` (##SUR_CHE_XII_V02_QP_E01_041SSS_S03.png" width="80%"> |
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