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FrankP

About TLC (curiosity)

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About TLC (curiosity)

 

So we do a lot of TLC analysis as well as melting point testing in my organic chemistry class this year. The reason I am asking more in depth on TLC is I get the concept of TLC. You use a board and solvent to extract and confirm purity of a polar substance based on the resulting Rf values. This makes sense to me through and through.

 

My curiosity is that I want to understand better the intricate workings of this. I am not good enough to look at the molecular structures of say for example Naphthalene, Benzoic Acid, Aspirin, Caffeine etc. and say ok out of these 5 the order should ideally be (X,Y,Z…)

 

I believe this stems from my lack of grasp on the solvents being used. I feel that still I am not confident in explaining why some substance is more ideal as a solvent than is another. I know it is based on affinity of that molecule and its polarity to the solvent. Example is why hexane is used in extracting non-polar molecules from water as it is a better solvent for such. I also understand that polar covalent bonds are water soluble while non-polar covalent are more soluble in oil.

 

I guess I am looking for suggestions on where to read more about TLC I looked in my colleges library yesterday but there was a book that was written in 1970’s and was extremely advanced for my base knowledge of organic chemistry or chemistry as a whole for that matter. This is my spring break week so I have some time to do some reading I know that when I come back we are going to be hammered with work and on the final there will likely be several questions that involve explaining TLC and how it works.

 

Thank you, in advance as always!

 

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I don't know about a specific book, but I would think that looking for general analytical books may be easier to read for a beginner. Or loot at chromatography books (or sections) as the principles are pretty much the same. In fact, I would recommend that you familiarize yourself with the principles of chromatography, as it makes it easier to understand the principles of a special case (such as TLC).

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Ok I will check to see if I can find anything online as it pertains to general chromatography first. I actually forgot that TLC is only one aspect of Chromatography, since it is the only form we use at my school. Thank you I appreciate it

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Not much has changed with the general principles of TLC since the 1970's, I wouldn't think. As CharonY suggested, I'd look up a book on chromatography and read up on that. The concepts will be the same.

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Introductory and intermediate laboratory books on organic chemistry sometimes cover this topic. For the example you gave, it would be difficult to put all of them into the correct order a priori. However, sometimes one can use general knowledge about intermolecular forces and general notions of polarity. For example, if I had two compounds that were nearly identical and one could donate a H-bond and the other could not, the one that can donate a H-bond is more polar and will have the lower Rf on silica. Of the compounds you listed, which one do you think would have the highest Rf and why?

Edited by BabcockHall

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