Reactions of the anomericcenter-I1
Reactions of the anomeric center-I 1
HHHHCH,OHCH,OHCH,OH000HOHOHOHHHSHHHHOHOHOHOHOHOHOHHHHHHOHβanomeropen-chainformα.anomerequilibrium in solutioncrystallizebelow98°Ccrystallizeabove98°CHHCH,OHCH,OH0HOHOHHH,OH,Oequilibrium mixture of α andβHHHOHO-HOH[α] = +52.6OHOHHHHOHpureβanomerpureαanomermp 146°C,[α]=+112.20mp150°C,[α]=+18.72
2
The anomeric centreOHOHH20HOCOHHOHOOHOHOHβ-glucopyranosea-glucopyranose62%38%AxialEquatorial3
The"anomeric centre"" O OH HO HO OH OH O OH HO HO OH OH H2O !-glucopyranose "-glucopyranose 38% 62% Axial&& Equatorial&&& 3
Acetal formation and hydrolysisMe.OMeOMe0R+HHOMe+ H+ROHOMeRReHHHHHMeOHOMeMeOMe+HORH+HRO=OMeRROMeOCH十HMeHHHH+HOHOMeH+ROHREOMeOHAH4
Acetal&forma1on&and&hydrolysis&& R H OH OMe H+ R H O O Me H H R H OMe MeOH + H+ R H OMe OMe R H OMe OMe H+ H+ R H O O Me H Me R H OMe HOH R H O OMe H H R H OH OMe H+ R H MeOH + O 4
Acetals and hemiacetals are in thesame oxidation state as carbonylsand it is therefore not surprisingthat they are readily inter-converted and you should think ofthe process of aldehyde-to-hemiacetal-to-acetal asonereversible rxn5
Acetals and hemiacetals are in the same oxidation state as carbonyls and it is therefore not surprising that they are readily interconverted and you should think of the process of aldehyde-tohemiacetal-to-acetal as one reversible rxn. 5