IAT IISER2026ChemistryGeneral Organic Chemistry
Consider the following silica-gel based thin-layer chromatogram of compounds A and B . Which one of the following statements is correct?
Options
- AA is more polar than B ; B has R_f = 0.33 .
- BB is more polar than A ; A has R_f = 0.75 .
- CB is less polar than A ; B has R_f = 0.75 .
- DB is more polar than A ; A has R_f = 0.25 .
Correct answer
B. B is more polar than A ; A has R_f = 0.75 .
Step-by-step solution
The retardation factor ( R_f ) is given by the ratio of the distance travelled by the substance to the distance travelled by the solvent front. R_f( A ) = 3.75 5 = 0.75 R_f( B ) = 1.25 5 = 0.25 Silica gel acts as a polar stationary phase. A more polar compound interacts more strongly with the silica gel and therefore travels a shorter distance up the plate. Since compound B travels a shorter distance ( 1.25 cm ) compared to compound A ( 3.75 cm ), compound B is more polar than compound A. Answer: B is more polar th