Question

slightly confused I thought Rf 0 was solid and Rf1 is slightly liquid please any help is greatly appreciated.

3. Two extreme values for the Retention Factor are 0 and 1 

a) Explain what each Re value means in terms of the substance's affinity for the mobile phase and for the stationary phase. 

b) Describe the features of molecules that would have these extreme Rr values under the conditions in this experiment: the solvent an 80:20 mix of petroleum ether and acetone, the TLC plate hydrated silica gel. 

4. For each spinach pigment shown below - draw circles around the polar and nonpolar regions of the molecule, and label each circled region with the type of intermolecular attractive force it could use to interact with the stationary or mobile phase. (For the chlorophylls, you're to assess only the organic portion of the compound, and not the Mg' Nitrogen complex at the center of the molecule) 

Then - explain (as thoroughly as you can) the relative distance that each pigment traveled on the TLC plate. 

Carotenes 

Chlorophyll a 

Answer 1

3) a) Rf=0: TLC is an adsorption chromatography. Rf value is the ratio of distance traveled by the spot to the distance traveled by the solvent front.
When any compound has Rf=0 this means the compound has not traveled at all any distance. This could happen, 1) compound is highly polar and has a very high affinity towards the polar stationary phase. 2) compound do not have any affinity towards the mobile phase at all 3) compound is highly polar in nature.

Rf=1: When spot moves along with the solvent front the Rf value becomes 1) This could happen because compound does not have any affinity towards polar stationary phase at all. 2) compound has a very high affinity towards the mobile phase. 3) compound is non-polar.

b) The solvent is 80:20 pet ether and acetone. Pet ether is very non-polar solvent and we are increasing its polarity by adding a little amount of acetone as a polar solvent. TLC plate is hydrated silica gel, means it is highly polar due to the open hydroxyl groups.
Rf=0: When Rf value is 0, this means compound is not moving at all with the solvent front. This could be because the compound is also highly polar.
Rf=1: If Rf is 1 this means compound is nonpolar and it moves along with the solvent front. It does not have any affinity towards the polar stationary phase.  

Carotenes The compound does not have any polar group such. In this molecule, we have all non-polar C-C and C-H bonds and hence it will not interact much with the polar stationary phase, however, it will have high affinity towards non-polar solvent. Hence it will most possibly move along the solvent front. This will give a high Rf value Chlorophyll a Non-polar CH, Polar Polar Polar CHs Non-pålar 20 Carbon chain

In the case of Chlorophyll, there are polar groups present along with the non-polar ring systems. These polar groups have a stronger interaction with the polar stationary phase and hence will have lower Rf value than that of carotenes.