Question

Hi,

I have some Organic Chemistry lab questions that I'm stuck on. Please explain in complete sentences

Thanks in advance

1. Describe the likely cuase and a reasonable solution for each problem encountered:

A. After spotting and developing a TLC plate, no spots are observed.

B. After spotting and developing a TLC plate, all spots moved along with the solvent front.

C. After spotting and develping a TLC plate, all spots are observed at the starting line.

2. What conclusion is justified if two substances rise at different rates on the same plate in the same solvent? What conclusion is justified if the two substances rise at the same level.

3. How can the R_F value be adjusted?

Answer 1

A)

your compound may not have any chromophore that will show in UV lamp

means suppose you take cyclo hexanol and spot in TLC plate compound might be there in the TLC plate but it is not possible to see in UV lamp at that time you have to choose proper staining agent, like KMNO4, Iodine, etc.

b)

suppose you are using more polar mobile phase than what you really required then your spots will move along with solvent front

in this case if you want to really see the spots raise the TLCplate in less polar mobile phase.

c)

in this case you might be using very less polar mobile phase than what you really want thts why spots are not moving

if you want to see tha spots increase little bit polarity your mobile phase then spots will start raising.

2

if two substances rise at different rates on the same plate in the same solvent means spot which is raising higher is less polar

spot which is at lower is more polar because TLC will work on absorption principal compound which is more polar will more sticky to TLC plate will move slowely, whare as compound which is less polar will sticky less to TLC plate and move more in the TLC plate.

if two are raising in the same level means both are in the same polarity.

Rf value can be adjusted by changing the polarity of the mobile phase.