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Topic: Why Use Benzene as an NMR solvent?  (Read 5390 times)

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Offline Flood18

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Why Use Benzene as an NMR solvent?
« on: June 29, 2010, 12:01:22 PM »
I recently came across a paper that used benzene as opposed to CDCL3 as an NMR solvent to improve the spectra...Why would this improve the spectra?  I assume it involves the special magnetic properties of benzene.  They also heated the sample to 70 C, if that has anything to do with it, thanks.

Offline DrCMS

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Re: Why Use Benzene as an NMR solvent?
« Reply #1 on: June 29, 2010, 12:16:38 PM »
I'd guess it was just a better solvent so they could dissolved more sample in the C6D6 and get a cleaner spectra that or the product had peaks in the same place as the CDCl3

Offline Flood18

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Re: Why Use Benzene as an NMR solvent?
« Reply #2 on: June 29, 2010, 12:25:04 PM »
Not really sure about that, just said it resolved the spectrum....Not too sure what peaks would have shown up at 7.3 though.

Offline g-bones

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Re: Why Use Benzene as an NMR solvent?
« Reply #3 on: June 29, 2010, 02:45:36 PM »
sometimes using benzene or toluene as a solvent helps to resolve aromatic protons more cleanly. 

Offline ardbeg

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Re: Why Use Benzene as an NMR solvent?
« Reply #4 on: June 29, 2010, 10:02:04 PM »
and if they heated it to 70 C then the CDCl3 would boil off and the spectrometer wouldnt be happy...

Offline orgopete

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Re: Why Use Benzene as an NMR solvent?
« Reply #5 on: July 05, 2010, 10:57:06 AM »
All solvents can have an effect on the chemical shifts of the solutes, even the TMS. That is why the solvent is noted in determining the NMR. If you obtain a spectrum of the same sample in a different solvent, it is not unusual to see small to unexpected shifts occurring.

Without the structure being given, it is very difficult to predict the purpose of using benzene. When I was in grad school (years ago), I used benzene to induce shifts in methyl ketones to determine whether they were axial or equatorial by the difference in the shift in benzene.
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Offline discodermolide

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Re: Why Use Benzene as an NMR solvent?
« Reply #6 on: July 10, 2010, 09:33:09 AM »
I recently came across a paper that used benzene as opposed to CDCL3 as an NMR solvent to improve the spectra...Why would this improve the spectra?  I assume it involves the special magnetic properties of benzene.  They also heated the sample to 70 C, if that has anything to do with it, thanks.

You get a so-called aromatic solvent induced shift. Depending on where the protons lie with respect to the pi system of benzene they move up or downfield, thus overlapping signals in CDCl3 may be resolved using this method.
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