gemar14
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Resolving power of TLC for R/S diastereomers?
I was wondering if anyone has had experience resolving R/S diastereomers on traditional TLC plates. I know that in general structural isomers and
alkene E/Z isomers can usually be resolved into two different spots on TLC plates, but what about R/S diastereomers? For example, if I had a mixture
of something like cis and trans 4-chlorocyclohexanol, would the polarity differences be enough to resolve the two R/S diastereomers on the TLC plate?
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numos
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Diastereomers have different chemical reactivity/properties and can always be theoretically separated with achiral techniques. In practice,
this is often highly substrate dependent and the best way to get an answer is to try it.
I would imagine that a mixture of simple alcohols like cis/trans chlorocyclohexanol could probably be resolved with the right solvent mixture. On a
more complex structure, all bets are off.
[Edited on 8-18-2022 by numos]
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Mush
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J AOAC Int
2001 Jul-Aug;84(4):1242-51.
Thin-layer chromatography--a useful technique for the separation of enantiomers
book
Thin Layer Chromatography in Chiral Separations and Analysis (1st edition) (2007)
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unionised
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Do you mean cis and trans isomers or do you mean R and S isomers?
You can, I guess separate mirror image pairs on TLC plates if you either use a chiral sorbent (I wonder if cornflour would work) or a suitable chiral
solvent.
Splitting cis and trans isomers is probably easier.
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Dr.Bob
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You can separate diastereomers on TLC, I do it often, but not easy, you need fine spots, long plates, and good methods. If you can use a low RF,
that often works better than a more polar solvent, but sometimes you must let the plate run several minutes. Often 25:75 Hexane:ETOAc works for
compounds like what you mention, but might need up to 50:50. Also harder to see the spots by UV than by KMNo4 or PMA.
I have separated diasteromers on flask chrom. in multigram amounts, so not easy (often the peaks overlap, so only about half of the fractions are
clean per run), but just depends on the loading and such. Good luck. I have some plates, fine spotters, and UV lamps if you need any.
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gemar14
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Quote: Originally posted by unionised  | Do you mean cis and trans isomers or do you mean R and S isomers?
You can, I guess separate mirror image pairs on TLC plates if you either use a chiral sorbent (I wonder if cornflour would work) or a suitable chiral
solvent.
Splitting cis and trans isomers is probably easier.
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In my example the cis/trans isomer would be an R/S isomer, but more generally I'm asking about diastereomers that differ only in the R/S configuration
of their stereogenic centers.
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Dr.Bob
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I have done a few that were R, S isomers, but had other set centers, so true diasteomers, as well as some cis, trans cyclohexanes with a mixture of up
and down alcohols.
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