Consider the following silica gel TLC plate of compounds A, B, and C developed i
ID: 788995 • Letter: C
Question
Consider the following silica gel TLC plate of compounds A, B, and C developed in hexanes:
a) Determine the R f values of compounds A, B, and C run on a silica gel TLC plate using hexanes as the solvent
b) Which compound, A, B, or C, is the most polar?
c) What would you expect to happen to the R f values if you used acetone instead of hexanes as the eluting solvent? (Think polarity of solvents)
Consider the following silica gel TLC plate of compounds A, B, and C developed in hexanes: Determine the R f values of compounds A, B, and C run on a silica gel TLC plate using hexanes as the solvent Which compound, A,B, or C, is the most polar? What would you expect to happen to the R f values if you used acetone instead of hexanes as the eluting solvent? (Think polarity of solvents)Explanation / Answer
Take a ruler and measure the distance between the origin and the solvent front: 2.75 cm. Then measure the distance between the origin and the center of spot A: 0.80 cm. Therefore the Rf for compound A is 0.80/2.75 = 0.29. Similarly, compound B travels 2.20 cm, and therefore the Rf for compound B is 2.20/2.75 = 0.80. Compound C travels 1.70 cm, and therefore the Rf for compound C is 1.70/2.75 = 0.62. Compound A is the most polar because it does not travel as far as the other two compounds. Remember, polar compounds stick to the adsorbent more readily, and thus do not travel as far and have a lower value for Rf. Acetone is a more polar solvent than is hexanes. If it were used to elute the same three compounds, each of the compounds would travel faster because the more polar eluting solvent is more proficient at eluting the compounds from the polar adsorbent. Since each compound travels faster, each compound would have a larger Rf value if acetone were used to elute than when hexanes is used to elute the TLC plate.