Question

List the polarity of the these pigment molecules. 1 = MOST polar. 5 = LEAST polar. And give reason why one would be most polar and most nonpolar?

A) B-carotene   B) Chlorophyll b C) Chlorophyll a D) Violaxathin E) Lutein

which of the pigments stated above would travel the farthest up the paper when separated using chromatography?

Answer 1

the xanthophylls contain oxygen- containing polar groups such as carbonyl, hydroxyl and epox- ide groups. Their position in the separation depends on the number and type of polar groups. Hydroxyl groups lead to a stronger polarity than carbonyl or epoxide groups. They therefore interact more strongly with the hydroxyl groups of the silica gel. The order of elution of the three xanthophylls lutein, violaxan- thin and neoxanthin can be explained by this, as an example: Lutein has two hydroxyl groups. Violaxanthin has two epoxide groups in addition, which leads to a stronger interaction with the stationary phase. Violaxanthin therefore runs more slowly than lutein. ,

we can deduce that carotenes are the least polar pigments (no polar groups), and xanthophylls are the most polar (two alcohol groups, one at each end of the molecule). ... Pigment C is likely to be chlorophyll, since it is more polar than carotenes but less polar than xanthophylls.

The distinctions between the chlorophylls, which are more polar than β-carotene is slight: chlorophyll a has a methyl group (Y=CH3) in a position where chlorophyll b has an aldehyde (Y=CHO). This makes chlorophyll b slightly more polar than chlorophyll a.

Violaxanthin > lutein >Chlorophyll b> chlorophyll a >B- carotene.

In general, the adsorptivity of compounds increases with increased polarity (i.e. the more polar the compound then the stronger it binds to the adsorbent). ... Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).so the order of speed is

carotene >chlorophyll a >chlorophyll b>Lutein >Violaxanthin