KETO ENOL TAUTOMERISM

Chromatography Forum: GC Archives: KETO ENOL TAUTOMERISM
Top of pagePrevious messageNext messageBottom of pageLink to this message  By vijay on Thursday, February 12, 2004 - 01:40 am:

Dear All,

when analysing a diketo compound {6-Chloro isating or 6-chloro-1H-indol-2,3-dione} we observed two major peaks in both gc and lc. some of our project mates telling that there exhibits a keto enol tautomerism exhibits and so the results.

I guess it must be some other process impurities simply based on that keto-enol tautomerism can't resolved well under chromatographic conditions.

we welcome your suggestion.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Benjamin on Friday, February 13, 2004 - 08:15 am:

Dear Vijay;

I have seen cases where there is separation of keto-enol species. This can happen as long as your mobile phase conditions allow for it, and as long as their equilibrium time is in the same order of magnitud as the separation times.

Other types of similar isomerisms are also commonly seen in HPLC, such as rotational isomers of Pro containing peptides, or of sterically hindered molecules.

I think you need to use some other spectroscopic technique to clarify your results. MS and NMR will give you valuable information, and UV in different solvents and at variable temperatures can also be helpful.

Good Luck

benjamin


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Russ on Friday, February 13, 2004 - 08:52 am:

Don't know how well your peaks are separated, and this may be more trouble than it is worth, but . . . If you can collect peak fractions and reinject them, and if the two peaks are tautomers, wouldn't you see approximately the same ratio of the two peaks for the reinjected sample regardless of the fraction injected? For example, if you have two peaks at approximately a 1 to 1 ratio and you collect and reinject peak A, wouldn't you see the same 1 to 1 ratio for the reinjection of "pure" peak A as the tautomeric equilibrium is "re-established"? If you don't, wouldn't that rule out tautomers? I'm probably overlooking something very simple here.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, February 13, 2004 - 11:18 am:

If you are seeing the equilibration between species, then you will see a curved valley between the two peaks, not a normal sharp valley. This is true especially if the two peaks are somewhat broader than expected. The equilibration valley may not be symmetrical.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By HW Mueller on Monday, February 16, 2004 - 06:52 am:

Itīs all a matter of how fast the equilibrium is in relation to the chromatography. If itīs relatively very slow you essentially get the chromatography of any two different substances. If the equilibrium is relatively fast you get one peak as if it were a single substance. Inbetween one can get smeared peaks as mentioned. I remember one example, namely osazones of ascorbic acid. We got two peaks corresponding to two geometric (inversion of N) isomers. When the two peaks were separatly collected and immediatly reinjected we got one peak, but if we waited a few hours before reinjection we got two peaks. The ratio of these two peaks will stay constant only after you reached equilibrium.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By vijay on Wednesday, February 25, 2004 - 10:51 pm:

Thanks for one and all for the valuable informations


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Michel Hachey on Thursday, April 1, 2004 - 06:08 am:

Would somebody be kind enough to give me a reference for an article that refers to an observed keto-enol tautomerism separation?


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