Chemical Biology 3OA3, September 2009 Page 28 E XPERIMENT 3 S UGAR A NOMERS : α-AND β-D-G LUCOSE P ENTA-ACETATE Introduction: D-Glucose is the most abundant sugar on the planet. It has been suggested that this is because all the substituents on the 6-membered ring are equatorial, making glucose the most stable structure possible. Notably, however, the stabilities of the two anomers, (isomers at the chiral C-1 acetal centre) are very similar. Thus, at equilibrium, the equatorial ( β ) and axial ( α ) anomers of glucose are present at similar concentrations. This unusual stability of the axial anomer has been ascribed to the “:anomoric effect”. In the axial anomer, the ring oxygen possesses one lone pair of electrons that is anti-periplanar to the C-OH σ bond. However, the in the β-anomer, there is no lone pair that is anti-periplanar to the C-OH bond: O OH OH O H O H O H O OH OH O H O H O H H+, H 2 O AXIAL OH @ C-1: alpha ANOMER stabilized by anomeric effect EQUATORIAL OH @ C-1:
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This note was uploaded on 01/08/2012 for the course CHM 30A3 taught by Professor Ricktroendle during the Fall '11 term at UNF.