Question

Which compound will have the larger Rf value on a SiO2 TLC plate using 10% ethyl acetate/hexane as eluent: 3-decanone or 3-decanol, toluene or benzoic acid, cyclooctane or cyclooctanone? Why?

Answer 1

A 10% ethyl acetate/hexane mixture is non-polar as it has 90% hexane and 10 % ethyl acetate. So, the non-polar compounds will travel farther along with the eluent(mobile phase). The more polar compounds strongly adhere to the adsorbent (silica TLC plate). Hence, the non-polar compounds of the mixture will have higher Rf value.

3-decanone has higher Rf value than 3-decanol.

Since, 3-decanol is more polar than 3-decanone, it is more adsorbed on silica plate and hence moves to a small extent along with the eluent. So, it has smaller Rf value.

Toluene has higher Rf value than benzoic acid

Since, benzoic acid is more polar than toluene, it adheres more to the silica plate and hence travels smaller distance. So, it has smaller Rf value.

cyclooctane has higher Rf value than cyclooctanone

Since, cyclooctanone is more polar than cyclooctane, it is more adsorbed on the TLC plate and hence moves to a small extent along with the eluent. So, it has smaller Rf value.