Hi,
I synthesized this structure which is combind with pyridine diamine and chloro acetylchloride.
Then, I have a question about the imidazole proton.
The proton could be shifted or not? If so, how can shift?
If not, where is the double bond in imidazole?
I'll wait your answers.
Thanks!
This type of "proton shift" is called tautomerism, and yes, it does take place. This compound will show up two sets of signals in NMR spectra due to existing facile equilibrium between these two inseparable forms. At high temperature, however, the equilibrium will be so fast, that the picture will be simplified, as only average spectrum will be observed (one set of signals).
To see the effect mentioned by Michael Rubin, use aprotic solvent for the NMR, such as dimethylsulfoxide. The chemical shifts are likely to appear above 10.5 ppm.
Dear Jubyeong Chae,
Prof. Rubin and Leonardo Silva gave you good advise. If you use dry DMSO-d6 as solvent, at ambient temperature you should observe a broad signal for the NH proton in the 13-14 ppm range. At lower temperatures, you might be able to see two signals owing to the two tautomers. Enclosed please find a reference and a spectrum of a similar imidazo[4,5-b]pyridine that shows a broad peak at 13.79 ppm (spectrum was recorded of a DMSO solution at 300.9K).
Good luck in your research! AF
The benzimidazole proton shift (PMR signal) is observed in down field with delta 12.15 ppm in DMSO-d6, The signal is little broader due to quadrupole moment of nitrogen & high electronegativity of the nitrogen.
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