I am conducting my research on organic synthesis of such compounds. after synthesizing these compounds, I have met some challenges specially in dissolving them with solvents specially right after purification process. the samples that I have purified are only slightly soluble to such solvents even with Dimethylsulfoxide (DMSO-d6). I need some enlightenment on what would be its cause with the NMR peaks or signals if the samples were only slightly soluble in such solvents.
you need to heat the sample try to dissolve....otherwise you cant clearly observe the splitting pattern.....
You may spectra may show absence of some low intensity signal in HNMR. In CNMR signal may be merge with noise due to low intensity.
Jerson, I assume you are talking about 1HNMR. If your samples are sparingly soluble in given solvent, you would see shimming problems. If your sample is NOT heat/acid/base sensitive, you could heat your sample or add ~10 mol% of acid or base to dissolve completely.
of corse yes,
if you simple is not completely dissolved in the D-solvent, the NMR spectra should be not good with absence of some signals or with broader peaks, so its better if you find the good solvent or you use heating
Thank you so much everyone for your suggestions. actually I already have a thought that HNMR would not be good and intensity of the samples may not be as clear as it would be if samples were completely dissolved. I just have to confirm it from other researchers because I have not yet encountered such problem. Furthermore, my samples were actually soluble in EtOH -d6 but EtOH is not available due to it is so costly here in the philippines so we tried other solvents for the analysis yet the results were not satisfactory. so I guess heating can be applied for this matter. Thank you so much.
You can go for solid state NMR.............. In solution particular minimum concentration is required other you can not get the proper NMR.... But you can try with more scaning.... You can not go for NMR with undissolved solid inside, as it is difficult to lock the sample during analysis.............. Solid state NMR is the best option for you.
Good luck............
If your sample is sparingly soluble, you can heat or centrifuge.
Or remove insoluble material byfiltration/ centrifuge and decant (which ever way possible), take the clear solution for NMR.. As the 1H-NMR doesn't need more sample, this may work for you... But for carbon you may need to find another solvent...
As above mentioned, you can try mixed solvents too
best luck!
Sometimes, the solubility of tested substance dramatically increase by using a mixture of solvents, e.g., DMSO and CHCl3, or DMSO and carbon tetrachloride. Please, try it to do initially on undeuterated solvents.
If the samples are soluble in EtOH, first try in methanol-d4. Removing the insoluble material by filtration or centrifuge and decant is not a good idea because you will be not sure whether the measured spectrum is a spectrum of your compound or of a spectrum of the soluble impurities!
In NMR spectrum of a partially soluble sample, i.e. oil or solids in the sample, you may see extra signals or uneven baseline. That is because the signals are dependent on nuclei environment, solvent vs. liquid or solid matrix.
If your sample is only partially soluble in a given solvent, the NMR spectrum will be only of the material in solution (plus the residual solvent signal(s). Samples containing suspended particles will cause broad lines and indistinct spectra. Filtration will remove undissolved material(s), but what you removed may be the compound of interest!
Best thing is to try different solvents . A list of NMR solvents are on NMR Solvents, www.chem.wisc.edu/.../nmr/nmr-solve... and on NMR Solvent Data Chart, www.isotope.com (Cambridge Isotope Laboratories).
You might try Dimethylformamide-d7; acetone--d6; toluene-d6 (v. good for both low and high-temperature work); CD3CN (when a more polar solvent is needed); THF-d8 (expensive); acetone-d6 (not as polar as others),;methanol-d4; CF3COOD only if your sample is stable in it. As Dimitrii pointed out, sometimes a mixture of solvents (e.g., DMSO and CDCl3 or CD2Cl2 might work. If your sample is stable at higher temps., carefully warming the solution might also solubilize the entire sample, but use caution when heating some solvents! If the sample dissolves at slightly higher temps., you may want to run the NMR spectrum at that temperature.
Good luck in your work!
Some times it happens with samples that contain some water. The turbidity will disappear with common drying agents (anh.MgSO4).
Or go for solid state NMR and compare the results.
wishing you success
Raju
The effect on the NMR signals if the samples are not well dissolved in such given solvents. The sample tube will not rotate properly as result there is no proper exposure of the sample to radiofrequency radiations. The broadening of the NMR signal occurs .
You will see broad signals, worse spin-spin decoupling, and generally spectrum will be with smaller signal to noise ratio. Noise will increase significantly.
If you have solid, or a viscous solution, or a gel, in general poor resolution and S/N will be obtained, with wide signals and bad lineshape and baseline.
there is a possibility of merging of peaks and U may not get splitting pattern correct, it happened with me, I would advise to go for temperature dependent NMR ( 60-70 oC in dmso-d6)
I would also like to suggest you to try mix solvents such as DMSO-d6 and CDCl3, or DMSO-d6 and Acetone-d6, toluene-d6 and Methanol-d4/CDCl3 or Acetone-d6 etc.
Thank you so much for your suggestions guys.. I hope your suggestions and knowledge can help me with what I am dealing right now. Thank you so much guys.. :) I would probably try to heat the samples with proper care or try to mix the solvents to achieve such solubility. thank you so much.
Hi Jerson,
I had a similar problem related to the solubility of my compound. One way to get around it is either by dissolving it in a solvent with a low boiling point, this will help in a quick dissolution of your compound or by sonication and finally, you can filter undissolved material but you might end up losing some of your product.
Good luck
My experience is that the NMR machine will give an error message. However, you could sonicate the sample, In some cases, gentle heating may assist in solubilizing the compound if the compound is stable to heat. But care should be taken to avoid decomposing the DMSO as this would give some signals for Me2S which could be trapped in the sample solution
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