Re: ORGLIST: Glucopyranose

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From: Jacob Zabicky (zabicky$##$bgumail.bgu.ac.il)
Date: Sun Nov 05 2000 - 07:22:35 EST

Hello Sharon,

Yes, of course, its classical: rotation angle of polarized light, measured
with a polarimeter. The term mutarotation has to do with the observation of
a changing angle when dissolving one of the forms in water, to get the
equilibrium mixture.

All the best,

Jacob

At 8:31 3/11/0, Sharon Stone-Elander wrote:
>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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Prof. Jacob Zabicky Tel. 972-7-6461271/6461062/6472754
Institutes for Applied Research Fax. 972-7-6472969
Ben-Gurion University of the Negev Private: POB 12366, Beer-Sheva 84863
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