[versyss]

I was wondering about how to choose a solvent to do TLC analysis.  I know it has something to do with the bonds and polarity, but I just want a clearer idea.  For example in lab I had a 2,4-DNP 2-pentanone and did three different type TLC analysis in pentane, diethyl ether and toluene.  Toluene turns out to be the best solvent, but why?  And why not the others? And why does the pentane hardly move up the TLC plate?

[movies]

Generally, you want to try and match the polarity of your eluent solvent roughly to the polarity of the molecule you are trying to move.  With the nitrogens and aromatic ring in your compound, you will need a reasonably polar solvent.  Pentane is about as non-polar as you can get, so it's not really surprising that your molecule doesn't move.  Diethyl ether is a bit more polar, but not all that polar as far as common organic solvents go.  Toluene is a funny solvent for chromatography.  You wouldn't expect it to be polar at all, but it tends to be able to move compounds that contain aromatic rings.  This is probably due to some kind of pi-stacking interaction.