Question

4. B-carotene and zeaxanthin are both yellow pigments found in plants. Which would you expect to have a higher R.? Which would you expect to elute from the column first? (2 points) p-Carotene Zeaxanthin

Answer 1

Rf value depends on the polarity of compounds. The more polar compound can be bound to silica gel. Then they will move slowly. So Rf value of more polar compounds will be less compared to Rf value of less polar compounds. In the given example zeaxanthin has two hydroxy groups. so it is highly polar compared to beta carotene.  zeaxanthin can be bound to silica gel through Intramolecular H- bonding between hydroxy groups of zeaxanthin and silica gel. Therefore the Rf value of zeaxanthin will be less. Beta carotene is a highly nonpolar compound. So Rf value of   beta carotene will be more compared to than that of zeaxanthin.

Beta carotene is a highly nonpolar compound. It can not be bound to silica gel. There fore Beta carotene is expected to elute first in the column chromotography.