Question

Comment on the characteristics (i.e. polarity) of the adsorbent and eluent that were used for the TLC that you ran. Under these conditions do polar or non-polar compounds have larger Rf values? Explain.

Adsorbent used: Silica Gel

Eluant used: Dichloromethane (CH2Cl2)

Answer 1

Due to presence of hydroxyl groups on the surface of Silica gel, it behaves as a highly polar adsorbent.

Dichloromethane is also a highly polar substance due to presence of highly electronegative Cholrine that tries to bring electrons shared between the C-Cl bond to itself by negative Inductive effect.

RF values signifies the strength of bonding of the eluant with the adsorbent. The stronger the bonding, the lesser its able to travel up the TLC plate. As "like dissolves like" any polar compound will be adsorbed greatly by silica gel thus will have lower RF values.

Hence, NON-Polar compounds will have larger Rf values