Question

Of the four compounds chlorophyll a, chlorophyll b, xanthophyll and beta- carotene, which is the most polar? Which is the least polar? Explain.

Answer 1

Both chlorophylls chlorophyll a and chlorophyll b contain C-O and C-N bonds (polar groups) and it is almost ionic, Chlorophyll a has a methyl group (-CH₃) at a certain place where chlorophyll b has an aldehydic group (-CHO), hence chlorophyll b is even more polar than chlorophyll a. But β-carotene is a hydrocarbon and is non-polar. It can be easily understand if we look at their structures. Xanthophyll is almost similat to β-carotene, but additional -OH group makes it more polar than β-carotene.

So order becomes from highest to least:

chlorophyll b > chlorophyll a > Xanthophyll > β-carotene

......↑.....................................................................↑...........

Most polar......>......................>.....................> least polar

HC N= LCOCH K MO Chlorophylla HCC сн. н ен, CH.CH ANNA COC Chlorophyll b 1600 CH, CH,

beta-carotene xanthophyll HO

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