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Author: Subject: How long can I wait before I take NMR?
Magelia
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[*] posted on 22-10-2012 at 10:34
How long can I wait before I take NMR?


Hi:

I just made my NMR and added my chloroform. I just saw the NMR machine is busy for the next two hours...

Can I afford to wait 2-3 hours before I take the NMR of my product? How about 2-3 days?

Thanks
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Ephesian
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[*] posted on 22-10-2012 at 10:54


I assume you used CDCl3

and yes, it should be fine



but if you don't want to trust me, save your sample, run a 1H-NMR. Then make a new sample and run an 1H-NMR and see if you have different resultant peaks. My guess is that nothing will be different. Just don't F(*K with you gradient shims

[Edited on 22-10-2012 by Ephesian]
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UnintentionalChaos
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[*] posted on 22-10-2012 at 11:16


If the thing that you dissolved in the chloroform is stable, then yes, you'll be more than fine. I've left (stable) samples in NMR tubes for weeks and as long as the caps fit tightly enough to keep the CDCl3 in (wrapping the top in parafilm helps), you're golden.



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DJF90
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[*] posted on 22-10-2012 at 11:35


I've had samples gone off in the NMR tube. Sometimes this is because the sample was light sensitive (e.g. phenylacetylene iodide), but chloroform is quite acidic and can cause troubles sometimes. Its worth noting that CDCl3 is not the only NMR solvent available, but it is one of the most common. Benzene-d6 often does a good job, and multiplets are often more spread apart, making asigning the peaks and multiplicities easier. It is alot more expensive than CDCl3 but worth it in the right instances.
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Magelia
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[*] posted on 22-10-2012 at 13:10


Thanks guys. Good stuff! I'll def keep that in mind!

Regarding a C13 NMR, what's a good standard amount of time to leave my sample in the NMR machine for?
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kristofvagyok
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[*] posted on 22-10-2012 at 13:29


Quote: Originally posted by Magelia  
Regarding a C13 NMR, what's a good standard amount of time to leave my sample in the NMR machine for?


It depends on a lot thing, if your sample is concentrated e.g. 80mg, then the C13 scan will be good in a couple on minutes e.g. 20. But if you make a really dilute sample with a few mg, then the whole night could be spent to get a good spectra.

And also if it is shimmed not correctly than your results could be thrown out on the window.

What NMR do you use? How much MHz? What software?




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Nicodem
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23-10-2012 at 11:57
Magelia
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[*] posted on 23-10-2012 at 16:16


I have a 400MHz.

I just took a look at my NMR spectra and it looks HORRID. Take a look at it... was it perhaps not shimmed long enough? I left it all night...

Weird.png - 74kB
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