Re: ORGLIST - orglist Digest - V01 #173

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From: Jacob Zabicky (jzabicky$##$etseq.urv.es)
Date: Mon Aug 17 1998 - 09:49:45 EDT



>Date: Fri, 14 Aug 1998 13:33:02 +0200
>From: DUFRASNE FRANCOIS <dufrasne$##$ulb.ac.be>
>Subject: specific rotation
>
>
>Hello everybody,
>
>I have a question, maybe somebody has an answer but, specially, an
>explanation.
>
>I thought that, for a diastereoisomeric salt (like norepinephrine tartrate),
>specific rotation of the separated molecules could be add to each other to
>give the specific rotation of the salt. I tried to calculate this with
>norepinephrine tartrate and found a result that is different from the
>experimental measurement. Can somebody give me an explanation or tell me
>where my reflexion is wrong.
>

The possible answer to your querry is that you are dealing wiyh the OR of
the ions and not of the pure compounds. Thus, norepinephrine is dissolved
as the norepinephrinium salt while tartaric acid as the tartrate salt. If
you add to this consideration of the "weak" nature of both the acid and the
base, you'll end up with solutions that their OR does not increase linearly
with concentration, due to the hydrolysis of both constituents.

So, find the OR of epinephrine in strongly acidic solution, that of
tartrate in both degrees of ionisation (requires two diferent pH values),
determine the pH of your norepinephrine tartrate, and try to sort out the
OR of the solution by considering all the species present.

All the best,

Jacob Zabicky



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Prof. Jacob Zabicky Fax. xx-34-977-559694
c/o Prof. Alberto Coronas Tel. xx-34-977-???
Department of Mechanical Engineering Private No.
Universitat Rovira i Virgili xx-34-930-119552
Cra. de Salou s/n
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Spain
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