My textbook states the thin layer chromatography could separate enantiomers only if both/or the mobile and solid phases are chiral?
Why so?
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$\begingroup$ Talking about enantiomers, we are dealing with optically active compounds. This unique physiology allows to rotate plane - polarized light in two opponent sides. Analysis of optically active compounds in complex samples is often based on chiral chromatography or capillary electrophoresis in order to separate the enantiomers. For this you require an opponent chiral reagent. The most common method is HPLC + CD detector. Anylizing the sample youll see negative & positive peaks for the opponent enantiomers, respectively. $\endgroup$– MabadaiApr 14, 2018 at 22:59
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1 Answer
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The reason is simple: the physical properties of chiral pairs are exactly the same.
So, for any given compound that is chiral, the melting point, the solubility, the partitioning between liquid and solid phase in a chromatography column etc. are all exactly the same for the pairs of chiral molecules. Simple physical processes can't distinguish the two molecules. The solvents and solid components in chromatography are rarely chiral, so they can't tell the enantiomers apart.
The only things than can are other chiral things. If the solid phase of a chromatography column were chiral (or the solvent, though that is a lot less common) then the column could separate the enantiomers.
Think of shaking hands. It is natural that a right handed person shakes hand with the right hand of another person but the interaction is radically different if they to shake hands with the other persons left hand. The interaction of chiral things (like hands) depends on chirality. But if you bump fists instead (fists being closer to a sphere which has no handedness) then it matters a lot less which hand your friend uses.
answered Apr 14, 2018 at 23:22