Question

What would be the result of using a very polar solvent like methanol (instead of ethyl acetate) to develop your TLC plates?

Answer 1

In in most lab applications, you will use standard phase silica plates. You will apply your reaction mixture in solution to the plate then "run" the plate by allowing a solvent (or combination of solvents) to move up the plate by capillary action. Depending on the polarity of the components of the mixture, different compounds will travel different distances up the plate. More polar compounds will "stick" to the polar silica gel and travel short distances on the plate, while non-polar substances will diffuse into the solvent and travel large distances on the plate. The measure of the distance a compound travels is called Rf. This number, between zero and one, is determined by measuring the distance the compound moved from the baseline (where it was originally spotted) divided by the distance the solvent moved from the baseline.

more polar solvent system results in a larger Rf.

polar solvents will usually move non-polar compounds to the solvent front and push the polar compounds off of the baseline.