Chromatography Forum

Hi, can anyone please advise: I know pi pi interactions are likely to occur between pi donor and pi acceptors. Is it feasible that pi pi interactions can occur between 2 pi donors, my own instinct is that they cannot, but alot of the literature I have been reading regards specific interactions of various column types suggests otherwise. Please advise.

http://www.sigmaaldrich.com/supelco/the ... 004web.pdf


Read the article on page 4 of this issue of The Reporter

Besides, who says anything about donation in van der Waals type of interactions?

Besides, who says anything about donation in van der Waals type of interactions?

I agree. I think that pi-pi interactions (i.e. between phenyl- rings) are also called: hydrophobic interactions,

Best regards

A further recommended read to all interested in phenyl columns would be:


Chromatographic classification and comparison of commercially available reversed-phase liquid chromatographic columns containing phenyl moieties using principal component analysis

Euerby, et al.

Journal of Chromatography A
Volume 1154, Issues 1-2, 22 June 2007, Pages 138-151

A good recent overview is Snyder, J. Chromatogr. A 1098 (2005), 123. A specifc article on pi-pi is Yang, J. Chromatogr. A 1097 (2005), 124. Or you can read an overview about stationary phases and method development in Neue, J. Sep. Sci. 30 (2007), 1611. Or in the Encyclopedia of Separation Science under Chromatography: Liquid: Mechanisms: Reversed-Phase

Thank you all for replying. However, I was wondering if further clarification was possible

This statement is taken directly from the paper in JCA by J.E Leon 841 (1999) 147
"An interaction between pi electron containing compounds is favoured when one of the compounds is electron rich and the other is electron poor. In these cases the stationary phase can act as a donor while the solute can act as a recipient. The stability of the pi donor pi acceptor complex is determined by the energy levels of the HOMO (donor) and LUMO (acceptor) respectively"

The second paper "Relevance of pi pi interactions of cyanopropyl and phenyl columns" seems to contradict this statement.
"Molecules with a more extended pi-electron ring system (or a greater number of aromatic rings) should be stronger pi-bases and therefore interact more strongly with either a cyano or phenyl column. Similarly, aromatic molecules substituted by nitro groups are stronger pi-acids, also resulting in stronger pi–pi interaction.
Any thoughts

Note that the first article says "favored", not exclusive, or such.
I would be very surprised indeed, if there were many substances that formed something that could honestly be called a pi-complex with the aromatic substituents in a phenyl column. If one would get a complex (that deserves that name) one may expect a stop or go situation (as in conventional affinity chromatography), not really a chromatography.
Now, one can imagine that there are stronger van der Waal forces toward electron rich aromatics as well as electron poor aromatics (electron density related to the immobilized aromatic of the stat. phase).
Anybody have some numbers?