Ch_322b_22.10

Ch_322b_22.10 - Some Other Reactions of Monosaccharides...

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Some Other Reactions of Monosaccharides Enolization, Tautomerization and Isomerization When D-glucose is dissolved in an aqueous solution of calcium hydroxide and allowed to react for a few days, several products are recovered including D-mannose (an aldohexose) and D-fructose (a ketohexose). Monosaccharides such as D-glucose react under basic conditions through enolate ions produced from the open-chain aldo- or keto- forms. epimerization at C-2 CH O = OH OH OH HO H H H H CH 2 OH D-glucose HO - H 2 O CH O OH OH OH HO H H H CH 2 OH : - CH O OH OH OH HO H H H CH 2 OH - enolate anion HO - H 2 O CH O HO OH OH HO H H H H CH 2 OH D-mannose
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CH O = OH OH OH HO H H H CH 2 OH : - CH O OH OH OH HO H H H CH 2 OH - enolate anion tautomerization and isomerization H 2 O HO - CH O H O H OH OH HO H H H CH 2 OH enediol (note: pK a ~ 9-10 ) HO - H 2 O CH OH O - OH OH HO H H H CH 2 OH CH OH O OH OH HO H H H CH 2 OH = : - enolate anion II H 2 O HO - O OH OH HO H H H CH 2 OH = CH 2 OH D-fructose By the above scheme, D-glucose, D-mannose
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Ch_322b_22.10 - Some Other Reactions of Monosaccharides...

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