An unknown mixture \"X\" was spotted on an alumina TLC plate alongside three kno

Question

An unknown mixture "X" was spotted on an alumina TLC plate alongside three known compounds (A, B, and C) and then developed in hexane. The resulting TLC chromatogram is shown below. Solvent Front Origin a. (3 points) Based on this chromatogram, you can conclude that unknown mixture "X" is most likely composed of b. (4 points) Estimate the Rf values for components B and C (you don't need a ruler, count squares, show calculation) c. (3 points) Which known compound (A, B, or C) is the most polar? d. (4 points) What would happen to the position sample B is we developed the plate using methylene chloride (a polar solvent)? 14. (8 points) Recalling that the specific rotation, (al, is defined by the following equation observed roataion aJp- a. Calculate the specific rotation of unknown compound Y if 15.0 grams of Y dissolved in 100 mililiters of isopropanol in a I dm polarimeter tube gave an observed rotation of 3.40. (show calculation) b. Calculate the optical purity if the specific rotation of a standard (pure) Y 24

Explanation / Answer

a. Since the mixture x spotbis at the same level of known compound B spot the mixture x is mainly composed of compound B.

b. Rf = distance moved by solute front/ distance moved by solvent front

So for compound B = 2 squares/ 9 squares = 0.22

Compound C = 6/9 = 0.66

c. Since hexane is nonpolar it dissolve non polar compounds( like dissolve like) hence such compounds move far from the origin along with the solvent. Polar compound dont move along with the solvent (nonpolar) hence compound B is most polar.

d. If methylene chloride is used since its a polar solvent dissolves more compound B (as it is polar) and move far from the origin along with the solvent and would have highest Rf value.

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