2) The following two solvent systems were found to separate compounds X and Y by

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?

Explanation / Answer

Q2) Compound Y is more polar than compound X.

X required 10:1 hexane :ethylacetate which has less percentage of polar ethylacetate to have optimal Rf range while Y required 10:4, that is more polar solvent mixture to get optimal Rf/.

Q3) To separate a mixture of X and Y , we need to first start with hexane :ethylacetate in 10:1 ratio so that all X will be eluted. ONce all X is eluted, then increase the polarity gradually by increasing the ethylacetate ratio, such that Y can be eluted.

If the gradient to start is 1:1 hexane, ethylacetate, both X and Y will be eluted together , no separation is possible, as the solvent is very polar , both are eluted.

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