Benzoin is more polar than benzil. To understand how we can determine this using TLC (Thin Layer Chromatography) plates, it’s essential to look at the structural differences between the two compounds.
Benzoin has a hydroxyl group (-OH) which contributes to its polarity. This functional group can form hydrogen bonds with solvents, increasing its polarity. On the other hand, benzil, which has two carbonyl groups (C=O), lacks this hydroxyl group and thus exhibits lower polarity compared to benzoin.
During a TLC experiment, a small amount of each compound is applied to a TLC plate, which is typically coated with a polar stationary phase. When a solvent (mobile phase) is used to develop the TLC plate, the more polar compound (benzoin) will interact more strongly with the stationary phase and move up the plate more slowly. In contrast, the less polar compound (benzil) will travel further up the plate as it interacts less with the polar stationary phase.
After developing the TLC plate, the distance each compound has traveled can be measured. The compound that travels less distance is the more polar compound, which, in this comparison, confirms that benzoin is indeed more polar than benzil. This method visually and practically demonstrates the polarity of different compounds based on their interactions with a stationary phase.