Question

2) During silica gel TLC analysis, when 2-propanol was used as a developing solvent, two substances moved with the solvent front (Rf = 1.0). Can you conclude that the substances are identical? If not, what additional experiment(s) would you perform? (5 pts).

Answer 1

- The presonce of thydroxyl group Co-H), which has a net dipole-moment towards the ongg makes the 2- propanol a bolas solvent as Compared to some other organic solvents o eig. hexane. The Dipole moment of a-Propanol 1.560, which is greater than hexome , ccly and benzene. Using z-propanol as a developing solvent means that it will move the compounds of Comparable polarity Since two substances moved with the solent front (Rf = 1:0), it concludes that the two Substances have a comparable polarity as that of zopropanol, but may not be identical. In such a case, it is suggested that one must decrease the polarity of the developing solvent either by mixing with a less polar or non-polar solvent with zopropanol or by checking the TLC behavior of the two substances by using a non-polar solvent as developing solvent. Then Increase slowly the polarity of the solvent say hexane by adding different proportions of Dichloromethance and after successive developments. In this way, the Rf of the two substances may be evaluated.