[vikram]

I have a host-guest solution in an aprotic solvent medium. I suspect that there is a probability of existence of anion- π interaction during host-guest recognition process. What is the simple and best approach to investigate this phenomena if at all it is existing? (I have read several literature where they solve crystal structure, do some computational study and all. I didn't obtain any crystal of host-guest complex.) What may be the best way to approach towards solving this problem.

[clarkstill]

I guess it depends on your particular system, and whether other forces are at play. You should be able to measure a binding constant, then ideally you would make a control compound for which the anion-pi interactions wouldn't form, but all other interactions remain the same to a first approximation, and compare the binding constants - whether this is feasible for your host/guest combo is another question.

You can look at NMR chemical shift changes in the aromatic ring, but it is extremely difficult to establish whether any such changes are due to a bonding interaction or just a proximity effect.

There's a decent review of methods here: http://pubs.rsc.org/en/content/articlepdf/2016/CC/C5CC09072E

but like you say, much of the work is through X-ray.

In short - good luck.

[vikram]

Your answer and link to the article is helpful.

Whatever NMR chemical shift prediction you suggested, same approach I followed at first. As there are two aromatic rings whose proton shift falls around very close to each other (around 8 ppm) it was very difficult to predict.

Let me wait for others reply too:)

Thank you:)

[wildfyr]

Really high field NMR (600+ MHz) could make it easier to watch such interactions and be sure of a change.

[clarkstill]

You could try UV-vis? If there's some interaction with the pi system you'd probably expect a change in the chromophore so there's a decent chance you could monitor binding that way.

[vikram]

Really high field NMR (600+ MHz) could make it easier to watch such interactions and be sure of a change.

Can you please mention in ppm scale?

[vikram]

You could try UV-vis? If there's some interaction with the pi system you'd probably expect a change in the chromophore so there's a decent chance you could monitor binding that way.

I have performed UV-Vis titration. But by the data obtained how can we visualize anion-π interaction?

[wildfyr]

I have no idea what the ppm difference will be, considering I have no idea what the molecule is, and such things are tough to predict anyways. I just know that high field NMRs will resolve peaks better, so small shifts in crowded areas can be observed more clearly.

[vikram]

I have no idea what the ppm difference will be, considering I have no idea what the molecule is, and such things are tough to predict anyways. I just know that high field NMRs will resolve peaks better, so small shifts in crowded areas can be observed more clearly.

No not like that. By your answer I thought that there is a certain chemical shift above which we can observe anion-π interaction more commonly. Is it so?

[wildfyr]

No clue.