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Friday, June 11, 2010

19F - 13C HMQC

If one has an NMR spectrometer with hardware capable of synthesizing and amplifying the frequency of 19F from the 1H channel and a broadband NMR probe whose 1H channel can tune down to 19F, then one is able to do 19F - 13C HMQC experiments. The figure below shows an example of a 19F - 13C HMQC spectrum collected on a Bruker AVANCE 500 NMR spectrometer using a 5 mm broadband probe. The fluorine spectrum is plotted on the top and the 13C[19F] spectrum is plotted on the side. The panel on the left shows the spectrum optimized for one-bond coupling, while that on the right shows the spectrum optimized for two-bond coupling. Note that the protonated carbons are doublets as proton decoupling is not possible in this configuration. The large signal, off scale in the 13C[19F] spectrum is due to the solvent (benzene-d6).

4 comments:

Ana said...

Very interesting, but I have some questions:
are you using 2 heteronuclear channels?
In my case, with a BBOF probe and 2 channels (1H/X), could it be also possible to run this experiment?
Are you using any filters?
Have you change the pulse program adding SWITO_F or whatever?
I would appreciate your answer
Thanks

Glenn Facey said...

Ana,

The data in this post were collected with a standard broad band probe with the broadband channel tuned to 13C and the proton channel "detuned" to 19F. In this configuration, 1H decoupling is not possible. A low pass filter was used on the BB channel and the 1H bandpass filter was removed from the 1H channel (tuned to 19F). On our instrument, the 1H amplifier is sufficiently broadbanded to permit amplification of the 19F frequency.

I suspect that this experiment could not be run on your BBOF probe as I believe that on such a probe the BB channel is used for 19F and the 1H channel remains fixed on 1H.

Glenn

Anonymous said...

Hi Glenn,

This is a very interesting entry. Concerning the set-up of this experiment, can I use a standard HSQC and change 'Nuc1' to '19F' or do I have to optimize other parameters as well. Thank you very much for your help.

Best wishes,

Lars

Glenn Facey said...

Lars,

I would use an HMQC rather than an HSQC as there are fewer pulses in an HMQC. There is a bit more to it than just changing nucleus 1 from 1H to 19F (see previous comments on this post for details).

Glenn