Question

Calculate the Rf value of the spot that corresponds to $\beta$ -carotene on the 7:3 Acetone:Toluene plate.

(TLC PLATES ARE CLOSE TO SCALE, NOT ACCURATE REPRESENTATION)

Answer 1

$\beta$-carotene is conjugated hydrocarbon of eight repeating isoprene units shows yellow-orange color on TLC as it

absorb violet, blue, and green light and reflects yellow, orange, and red.

R_f = (distance traveled by the compound)/(distance traveled by the solvent front)

Here in the given TLC (middle), distance traveled by the compound (Yellow spot corrosponding to $\beta$-carotene) = 5.2cm and distance traveled by the solvent front = 6cm.

Hence, R_f = 5.2/6 = 0.87

The quetion is asked on the basis of 7:3 Acetone:Toluene solvent phase where as in picture TLC shows 9:1 Toluene:Acetone system. I am assuming that answere is needed on the picture.