A chemist performed the reaction shown below. He then wanted to separate the mix

Question

A chemist performed the reaction shown below. He then wanted to separate the mixture using column chromatography. In his protocol he used silica as the stationary phase and a mixture of hexanes/ethyl acetate (75:25). Assuming the reaction did not go to completion and starting material is present in addition to the three product, which fraction would contain which compound? Explain your answer. What would be the consequence of changing the mobile phase to a 50/50 mixture of hexanes/ethyl acetate rather than 75:25? Would the order of elution change (the order in which the compounds come out of the column)? Explain your answer.

Explanation / Answer

Mono substituted and di substituted products are polar compounds where are trisubstituted product is non polar compound. So non polar compound eluted first because it less affinity towards column. Silica gel has polar nature so it has greater affinity towards polar compounds.

Order of elution is

First fraction contains tried substituted product.

Second fraction contains di substituted product that is di nitro benzene.

Third fraction contains nitro benzene (mono substituted product)

If we change the composition of mobile phase there is no change in order of elution.

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