Question

Which compound would have the higher Rf value- Cholesterol or Cholesterol Stearate? Explain why (TLC analysis, Polarity, etc).

Answer 1

Cholesterol is an alcohol with long carbon chain in it. The only polar bond in the cholesterol molecule is the O-H bond and it is much polar than any carbonyl bond due to high electronegativity difference.

Cholesterol stearate is another ester with only polar bond of ester. Stearate is derived from stearic acid which is having long chain of carbons. Thus in total there are 45 carbon units in this ester molecule. Thus it increases the non polarity.

On a TLC plate, non polar compound rises with non polar solvent and polar compound is stuck to polar silica plate. Thus polar compounds travel less distance and thus low Rf value than non polar one. It means Cholesterol will have lower Rf value than Cholesterol stearate