I found NMR In CDCl3, an unknown peak observed at 0, -5, -10, and -15 degrees celcius. The peak value is 5.1 ppm broad peak, which is not observed in the room and high temperature. Please suggest to me what is that peak with some references.
Thank you so much in Advance.
You don't say what your sample is. Is this supposed to be pure CDCl3?
Assuming that you have a sample dissolved in CDCl3, it could be an exchange-broadened peak. That might explain why it disappears at room temperature where it may be so broadened that it practically disappears.
For a more qualified answer, please provide more information about the sample.
Thanks for your answer. My Sample is a Supramolecular compound having M.W. 1904 with Amide and Ether linkage and no halide functional group. At room temperature, the NMR peak is a perfect match with the expected. But, in My Compound study, I check lower temperature spectra and I found an unknown peak at 5.1, unable to identify what it is... (CDCl3 peak is observed in all spectra at 7.24, no problem in it)
Hi Krishna Borde . I think I know what it is, as I encountered the same problem some years ago. It is dichloromethane included in your supramolecular compound (a pillar[5]arene derivative?). In CDCl3, dichlormethane should appear at 5.30 ppm (http://ccc.chem.pitt.edu/wipf/Web/NMR_Impurities.pdf) but the aromatic building blocks of the pillararene host provides a strongly shielding environment, shifting the peak significantly upfield.
The dichloromethane (DCM) comes from the synthesis of the pillararene. DCM is strongly bound to the cavity of pillar[5]arene and can be very difficult to remove. I had to heat the sample to 190 degrees for two hours to remove most of the DCM!
All of this is explained in the Supporting Information of this paper which also contains NMR spectra and thermogravimetric analysis:
dx.doi.org/10.1021/acs.jpcb.5b02515
The Supporting Information is accessible for free.
Please let me know whether my guess is correct :)
I thanks everyone professors for helping me. As I studied different ways, I conclude that At lower temperature, the H2O exchange the Dutarium to form HDO and D2O and the peak observed around ~5 PPM (http://ccc.chem.pitt.edu/wipf/Web/NMR_Impurities.pdf). Also as Professor Christian told, I found a very small peak of DCM in my supramolecular compound having a peak value of 5.2 ppm. (very sharp peak). Here I attached a spectrum of -5 degree Celcius. (HDO peak at 4.95 and DCM peak at 5.03).
So, these broad spectra belong to HDO and the small sharp spectra is DCM.
Water in CDCl3 typically appears at 1.6 ppm. There would have to be a lot of water for the shift to be at 4.95 ppm
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