Question

2) The following two solvent systems were found to separate compounds X and Y by flash chromatography: • The solvent that placed X in the optimal Rf range is 10:1 hexane: ethyl acetate • The solvent that placed Y in the optimal Rf range is 10:4 hexane: ethyl acetate Which is the more polar compound, X or Y?

3) In order to separate a mixture of X and Y as in problem (2) by flash chromatography, you decide to do a gradient elution.

Which solvent system must be used first?

Which compound will elute from the column first (assuming you chose the correct solvent)?

You accidently set the gradient to start with 1:1 hexane: ethyl acetate. What would happen? Will there be any separation? Why or why not?

Answer 1

2) Which is the more polar compound, X or Y?

answer = Compound Y is more polar compound as percentage of ethyl acetate used is more in eluting this compound.

3) Which solvent system must be used first?

answer = solvent 10:1 hexane: ethyl acetate should be used first. ( reason: this is non polar as ethyl acetate is less in this system)

Which compound will elute from the column first?

answer = compound X will be eluted first from the column. ( compounds which are non polar elutes first from the column)

You accidently set the gradient to start with 1:1 hexane: ethyl acetate. What would happen? Will there be any separation? Why or why not?

answer = there wont be any separation of the compounds X and Y as the polarity of this solvent system exceeds the polarity at which the compounds X and Y moves and hence both the compounds will come out from the column as the mixture.