Which compounds generally have the lowest Rf values on silica gel TLC?

Which compounds generally have the lowest Rf values on silica gel TLC?

• A. The most polar compounds
• B. The least polar compounds
• C. Aromatic compounds
• D. Highly nonpolar compounds

Answer: (A)

On silica gel TLC, the stationary phase is polar, so compounds that are more polar interact more strongly with the surface. These strong interactions—like hydrogen bonding and dipole attractions—hold the polar molecules back, so they travel the shortest distance with the developing solvent front and end up with the smallest Rf values. In contrast, nonpolar compounds don’t stick to the polar silica as much, so they move farther with the solvent and have higher Rf values. Aromaticity alone isn’t a reliable predictor of Rf because aromatic compounds can be either polar or nonpolar depending on their substituents. So the most polar compounds tend to have the lowest Rf on silica gel TLC.

On silica gel TLC, the stationary phase is polar, so compounds that are more polar interact more strongly with the surface. These strong interactions—like hydrogen bonding and dipole attractions—hold the polar molecules back, so they travel the shortest distance with the developing solvent front and end up with the smallest Rf values. In contrast, nonpolar compounds don’t stick to the polar silica as much, so they move farther with the solvent and have higher Rf values. Aromaticity alone isn’t a reliable predictor of Rf because aromatic compounds can be either polar or nonpolar depending on their substituents. So the most polar compounds tend to have the lowest Rf on silica gel TLC.