Question

can you please answer all

1. When you run a TLC of the reaction in ethyl acetate : hexanes 1:1, the plate below is produced. Give a solvent system that would be expected to produce greater separation and a BRIEF (8 words) justification about your choice. (5 points) 7 6 5 4 3 b. Calculate the R for the bottom spot. (5 points) c. Which compound on the TLC plate is the most polar? (5 points) 2. Why is it important to mark the solvent front when you remove you TLC plate from your beaker? (5 points) 3. Why is it important to place a small spot of compound on the TLC plate? (5 points)

Answer 1

1. A) From given system of ethyl :hexane 1:1
That is, 50% system is too much polar for given compounds .To get better separation TLC should be run in less polar system so that Rf of the compound will be less and separation will be more .The recommended system should be 30% ethyl acetate 70%hexane which is less polar than previous one.It will give better separation .

B) 8.5/9.5=0.89

0.89 is the Rf of 3rd compound.

C) The compound which has low Rf are generally polar.

In this case spot no 3 is polar.

2. When solvent front is marked we are able to decide to which  extent the solvent should be moved on TLC. If it is not marked then some times there is a possibility of running over TLC which will result in poor separation .
If we have to run TLC two times in the same solvent system then it is very difficult to remove TLC without marking the solvent front.

3. Small spot have results in less spreading of compound on TLC when it travels along with solvent system. Large spot have high probability to spread which will result in merging of compounds on TLC.

4. After chromatographic separation we have to take TLC of all the test tubes.
Then we have to check the given reaction mixture is separated or not based on their Rf . When we are able to find the test tubes containing same compound showing same Rf from the series of test tube. Those test tubes are selected and combined to evaporate on rotary evaporation.

5. Generally acids are polar in nature so silica has little effect on their movement as silica is also acidic in nature it moderately bonds to acids. Hence generally acids move slowly from silicagel columns. Even some times it will require polar system to remove acid from coloumn.

6. Ethyl acetate is more polar solvent then Hexane, as esters are more polar then long chain compounds. Ethyl acetate as a polar solvent allow better separation of polar compounds because the compounds interact with polar solvents more than non-polar solvents which allows them to elute further on the TLC plate.

And also, Polar dissolve in polar and nonpolar dissolve in nonpolar.

7. Recrystallisation is less time consuming and requires less solvent and gives pure product which will save time and resources for companies hence, crsytallisation is preferred over chromatography.