Re: ORGLIST: Glucopyranose

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From: Sharon Stone-Elander (sharon.stone$##$ks.se)
Date: Fri Nov 03 2000 - 02:31:44 EST

Hi!
Any other (besides NMR) way of observing the alpha/beta interconversion in
water or in other media?
-Sharon

>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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