07-08-04 00:25
No 518030
As I understand it, the issue of a molecules polarity is more complicated than just polar or non-polar.
see here: http://www.wcrl.ars.usda.gov/cec/java/so
As like dissolves like, when doing extractions from plants it would seem like one would want to know the polarity index of the molecule(s) that are of interest to the extractor so that the solvent with the closest polarity index could be selected.
So therefore it would be useful to know how to calculate the polarity of large, polycyclic molecules.
If someone could explain this concept to me, I would be most grateful. I have been looking on and off for this information for a while now, and have not found anything that seems like it would be applicable to the larger molecules that interest me (mostly polycyclic terpenes). I want to go beyond just polar and nonpolar and make selection of solvents more specfically directed to what is being extracted.
Hope this question isnt too basic.
(Chief Bee)
07-08-04 01:01
No 518042
So therefore it would be useful to know how to calculate the polarity of large, polycyclic molecules.
Definitely, such a discovery would be worth a small fortune.
However, there are no computational methods available which rivals empirical testing using TLC.
The Hive - Clandestine Chemists Without Borders
(Hive Bee)
07-08-04 07:00
No 518100
Thanks for the reply, Rhodium.
Hmmm. That's interesting and surprising to me that there is no easy way to determine a molecules polarity from knowing its structure. What exactly are the complicating factors that make it impossible to do this?
I was expecting to find out that there was some formula into which one could plug in stuff like charge difference across each bond, bond angles, distances of atoms from one another etc... So what else is there to factor in to determine the polarity of a molecule.
Is there any way to even approximate solubilities by looking at molecular structure? What other factors would need to be factored in besides charge difference across the molecule? (size of molecule, presence or absence of specific functional groups, what else?). Would the way that the molecules orient themselves in a given solution also be an issue?
Have any attempts been made at developing a predictive algorithm for the solubility of one molecule in another?
If anybody has any leads, they would be most appreciated. Trying to work out a way to make reasonably accurate predictions of solubility would be a most interesting project. I am sure its way over my head if nobodies done it already, but I would love to give it a try. If its all physics, then there must be a way to predict solubility.
(Stoni's sexual toy)
07-08-04 10:58
No 518139
I think I've seen methods to calculate polarity, but that's not necessary. Some big molecule could still be quite insoluble in a certain solvent with a very close polarity index, since many other factors determine if a compound is soluble or not. In the real world you usually can get away with using the common standard solvents without bothering about polarity index etc.
I don't remember seeing that polarity index stuff before.
Solvents are usually rated according to their dielectric constants.
BUSH/CHENEY 2004! After all, it ain't my country!
www.american-buddha.com/addict.war.1.htm
(Hive Bee)
07-08-04 19:01
No 518183
I wonder how this software works:
http://www.pion-inc.com/Absolv.htm
(Wizard Master)
07-10-04 08:05
No 518503
The solvent serves the dual function of solvating each individual charge of the molecule, which determines the self-energies of the charges, and screening the interaction between charge pairs. The electrostatic energy of a system of charges can be calculated by integrating the energy density of the electric field...
http://anusf.anu.edu.au/~vvv900/Effectiv
http://anusf.anu.edu.au/~vvv900/Effectiv