The \"stationary phase\" silica gel (commonly referred to as \"SiO_2\") found on

Question

The "stationary phase" silica gel (commonly referred to as "SiO_2") found on your TLC plate is a network of tetrahedral silicon that presents silanols (hydroxyl groups bonded to silica) at its surface. When compounds are dissolved in the "mobile phase" solvent that is pulled up the TLC plate by "capillary action, " the compounds interact with the silica surface. Each compound may spend a certain amount of time physically adsorbed to the surface of the silica gel or dissolved in the solvent, depending on its solvent miscibility. The stronger the interaction (attractive forces) between a given compound and the silica surface, the lower the Rf for that compound. Explain the difference between the Rf of the starting material and the Rf of the product. How might you increase the Rf of the starting material?

Explanation / Answer

3. Rf values are dependent upon the interaction of compounds with the stationary phase and the mobile phase. Here, the products are dichloro compound which is less polar than the starting material dihydroxy compound and thus product would have a higher Rf than the starting material.

4. The Rf of the starting material can be increased by increasing the polarity of the mobile pase from 5% ethylacetate in henxane to say 20% ethylacetate in hexane.

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