Re: ORGLIST: Glucopyranose

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From: ddd (sushilenterprises$##$bol.net.in)
Date: Fri Nov 03 2000 - 23:12:23 EST

sorry, not interested ,dont send us any mail.
-----Original Message-----
From: Soren R. Jensen <oksrj$##$pop.dtu.dk>
To: Multiple recipients of list orglist <orglist$##$dq.fct.unl.pt>
Date: Friday, November 03, 2000 12:40 AM
Subject: Re: ORGLIST: Glucopyranose

>Sharon,
>You can of course follow this mutarotation by measuring the specific
>rotation of the equlibrium mixture over 5-10 hours. - Soren
>
>At 08:31 03-11-00 +0100, you 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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