Question

Overall concept: Chromatography (concepts, TLC, GC; reverse vs. normal phase); compare relative behavior of compounds on the basis of structural features (e.g. hydrophobic vs. hydrophilic etc.) Mostly need help on comparing the relative behavior of compounds on the basis of their structural features. Need to be able to answer this: given multiple structures, with certain recognizable function groups, try and sort them according to their predicted relative Rf in given chromatographic conditions. Which one will run the fastest in a tlc? Or in a GC?

Answer 1

From tlc we can only predict the polarity of a molecule. The compounds having polar functional group( hydrophilic) will cover less distance from the base line than the compounds having non polar functional groups( hydrophobic). The reason behind it is polar compound will react with silica on the tlc and will bind to the tlc plate. So they need more time to move upwards i.e against gravity.