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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: kriggy on January 19, 2018, 03:00:41 AM

Title: CFCl3 as 19F NMR reference
Post by: kriggy on January 19, 2018, 03:00:41 AM

Hey, I need to measure some 20 samples with freon as a reference but I wonder.. how do you work with it when the bp is 24°C which is pretty much laboratory temperature. Is there ia problem with evaporation from the NMR tube in general? Or it doesnt matter since F NMR is quite sensitive. I would like to put my samples into autosampler when I get the freon from sigma but I worry that it would evaporate from the sample by that time.

thanks

Title: Re: CFCl3 as 19F NMR reference
Post by: Flatbutterfly on January 26, 2018, 02:11:14 PM

For recording NMR spectra of volatile samples use the special WILMAD NMR tube for the purpose:
http://newera-spectro.com/controlled-atmosphere-valve-cav

They are expensive and like all NMR tubes they are fragile, so purchase three and allow for breakage.
Before that we flame sealed tubes on the vac line (sample at liq N2 temps); the tubes had a Pyrex top with a constricted neck (made in-house).  Run your spectra at 0°C.

Why aren’t you using hexafluorobenzene, C6F6, as the ref?  Commercially available (Sigma-Aldrich) mp and bp similar to C6H6; δ -164.9 (vs CFCl3)   

Title: Re: CFCl3 as 19F NMR reference
Post by: kriggy on February 01, 2018, 02:52:07 AM

I did run it without standard but we got one spectra measured somewhere else with CFCl3 as a standard so I have to re-run all of them. I didnt think of other standard than this one. Probably could have saved me some time.