From: Soren R. Jensen (oksrj$##$pop.dtu.dk)
Date: Thu Nov 02 2000 - 12:53:57 EST
Ashutosh,
It is true that the equilibrum mixture of alpha/beta-glucopyranose is ca.
40/60 in water; this can be seen by dissolving crystalline glucose in D2O
and immediately running the NMR spectrum to give a spectrum of the almost
pure alpha form. - However, after about 10 h the above eq. mix. is reached.
This is partly due to steric effects, partly to the "anomer effect" [cf.
J.March (3rd ed.) p. 128].
The former demands an quatorial position of the 1-OH group, the latter an
axial. However, in a very polar solvent like water, the "anomer effect" is
rather weak and the result is the above percentages in the mixture. - Soren
At 23:08 01-11-00 +0530, you wrote:
>In an equilibrium solution of alpha and beta D-Glucopyranose there is a
slightly more percentage of the beta isomer.Is it due to some steric effect
or are some other factors involved too.
>Thanks
>Ashutosh S. Jogalekar
>Department of Chemistry
>University of Pune
>India
<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>
Soren Rosendal Jensen tel: +45 45252103
Dept. of Organic Chemistry fax: +45 45 933968
Kemitorvet, Build. 201
Techn. University of Denmark
DK-2800 Lyngby, Denmark
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