Hello,
I am trying to identify the formation of a synthesis product. Knowing the precursors, I focused on the identification of the H-C long-range coupling between sites (a/b) and (a/c) using [1H-13C]-HMBC and HSQC (to help in the assignment procedure). However, the 1H and 13C chemical shifts of the alkyl side chains of the imidazolium ring are very similar and it appears that there are other signals than those of the synthesis product (the synthesis is supposed to be clean as no substances other than the precursors have been used and it happens in one step).
Also, does the presence of nitrogen hampers the efficiency of polarization transfer ?
You can find a PDF where everything is explained in a schematic way.
Thank you for considering my question.
Please look at the following below attached files which may help you in your analysis.
Thanks
searching for a CH3 signal in the carbon spectrum might help. Educt signals can be identified by signal increasing after adding a small amount and remeasurement. If the signals are broad by exchange phenomenons measurement in acidic solvent (CF3COOD, DCl ) could be the solution.
Good luck!
Isam Eldin Hussein Elgailani Thank you for the provided documents.
Gerhard Krack Thank you for the hint. The only drawback is that, educts and the product are not miscible (I'll have at least two phases in the NMR tube).
Dear Clemens,
I thought about 15NHMBC, but then I didn't know which parameter set would be appropriate. Thank you Clemens, helpful as always.
(The ionic liquid has a good solubility in water and it becomes much less viscous)
Salem Baroudi , I think a good strategy is doing a DOSY experiment and comparing the diffusion of CH3 signal with the CH, which are signals with different chemical shifts. If the reaction indeed succeeded the mobility of all of the signal of the same molecules will be the same. Such an experiment would spend 10 min. A Bruker experiment stebpgp1s is enough, TD 32K x 16; p30 = 800 us; d20 = 70 ms; d16 = 200 us. You have to do "dosy 2d" command, instead of zg, to acquire. In order to process, you can make comparisons of the first 1D spectra generated (efp;apk;absn) with the last. You have to apply multiple display and scale one of the spectrum until it has the same intensity of the other, for one of the peaks. Automatically, the intensity of all the peaks from the same molecule will also be equal, in the two spectra. Signals of other molecules (with different diffusion), will not present the same intensity (see attached). If the attenuation of the signals was not higher enough to separate the different molecules, try other p30 and d20 values (higher values are required for polymers, as example). There are also ways to plot the DOSY results in 2D.
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