posted on 2021-07-26, 17:03authored byArtem
N. Fakhrutdinov, Bogdan Ya. Karlinskii, Mikhail E. Minyaev, Valentine P. Ananikov
The analysis of products synthesized
by Cu-catalyzed click reactions
can be complicated due to the presence of metal impurities in isolated
substances, which may “selectively” distort some signals
in NMR spectra. Such a pronounced impurity effect was found in both 1H and 13C NMR spectra for a number of 1,4-substituted
1,2,3-triazoles. Recording of the full undistorted spectra is possible
with additional product treatment, with more thorough purification,
or by recording the spectra at low temperatures. The reasons for the
distortion and disappearance of signals have been thoroughly studied;
it was shown that impurities of paramagnetic metal ions in small amounts
lead to this effect. Here, we want to deliver a warning message to
the community: when all NMR signals in a spectrum are distorted, this
situation is easy to detect. However, if only a few signals are “selectively”
removed by impurities and the rest of the spectrum appears normal,
this situation is much harder to notice. Therefore, incorrect conclusions
about chemical structure may be obtained. Here, we demonstrated the
example of Cu2+ ions, but one may anticipate a similar
effect for other paramagnetic metal contaminants if the organic molecule
has a functional group capable of coordination (heteroatom or a multiple
bond).