October 15, 2019, 07:27:15 AM
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Topic: Identification of a molecule in a complex organic solution using NMR  (Read 2956 times)

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Offline acef2104

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Dear all,

I have stumbled an interesting conundrum at my workplace - a lab managed to identify using HNMR and CNMR a particular molecule (e.g. butanoic acid) in a solution containing more than 50 different organic molecules. I know from my own chemistry background that it would be very messy to determine a single molecule in a very complex mixture but has times changed? Can you do this now instead of the traditional GCMS (or LCMS?)

If it is not possible, would appreciate if you can point me to a reference in the net because I've been trying to find it in Google and I haven't gotten any hits.

Thank you !

Cheers,
AC

Offline hypervalent_iodine

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Re: Identification of a molecule in a complex organic solution using NMR
« Reply #1 on: June 04, 2018, 02:29:53 AM »
I suppose it would depend on the relative concentrations, what else is in there, and whether or not they were expecting butanoic acid. In general, I would say it is fairly dubious to use NMR for singling out and identifying one compound from a complex mixture. You would be better served using something like GCMS, LCMS, or HPLC-MS. You can couple these to NMR as well.

Offline wildfyr

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Re: Identification of a molecule in a complex organic solution using NMR
« Reply #2 on: June 04, 2018, 10:25:05 AM »
I agree, while it may be possible if you knew exactly which molecule to hunt for, it is still a really difficult method compared to various forms of MS.

Offline kriggy

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Re: Identification of a molecule in a complex organic solution using NMR
« Reply #3 on: June 05, 2018, 02:16:10 PM »
Depends on what are the stucture of other molecules. Mixture of 50 will give you crazy spectra but you MIGHT get away using diffusion NMR (which AFAIK, takes about 1-2 days of NMR time). Also, it might be possible to derivatize the acid to get some other structure that can be more easily identified with NMR like converting it into some silylated ester that will have chemical shifts very low and then compared to standard of pure sililated derivative or converting it into some ester/amide with fluorines so you could use 19F NMR for that (again compared with standard)

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