# RE: ORGLIST: rotation

From: Ilya Avrutov (IAvrutov\$##\$dalton.com)
Date: Fri Jun 10 2005 - 10:31:26 EDT

Dear Uno,

I did not find the text of IUPAC rules from original, but in the site =
http://www.sciencecollege.co.uk/SC/iupac_nomenclature.html#optical I've =
found the following equation (this site is explanation of IUPAC =
nomenclature for students):

α = 100 x rotation (o) / path (dm) x concentration (g 100mL-1).

So it's just a matter of plugging in the figures given. Note that path =
lengths are usually quoted in cm, so divide them by 10 to give them in =
dm. Concentrations are usually quoted in molar, so you may need to =
multiply by the RMM to give you the concentration in g L-1 then divide =
by 10 to convert to g 100mL-1.

The next reference is an instruction for authors from Helv. Chim. Acta =
(http://www.helvchimacta.ch/instru.htm)

"b) The symbol c is used in connection with the specific optical =
rotation [α]; it is defined as mass of substance (in g) in 100 ml of =
solution. The quantities l and d in [α] = 100 · α/l · c or =
[α] = α/l · d are given in dm and g/ml (kg/m3), respectively."

I think here is the source of the confusion. If you use equation [α] =
= 100 · α/l · c , the concentration is expressed in g/100 ml. In =
case you use equation [α] = α/l · d, it is measured in g/ml.

Best regards,
Ilya

-----Original Message-----
From: everybody-bounces\$##\$orglist.net =
[mailto:everybody-bounces\$##\$orglist.net] On Behalf Of Uno Maeorg
Sent: Thursday, June 09, 2005 11:16 AM
To: everybody\$##\$orglist.net
Subject: ORGLIST: rotation

Hi,

Could you tell please what is the correct definition of concentration by =
determination of optical rotation alpha.Textbooks are giving c in g per =
mL, Eliel's Sterochemistry tells g per L, Koskinen's book gives g per =
100 mL.
I hope somebody knows the correct answer what is compliant with IUPAC =
rules.

Regards Uno

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