High resolution carbon-13 nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism was written by Faure, Robert;Vincent, Emile Jean;Rousseau, Andre;Claramunt, Rose Maria;Elguero, Jose. And the article was included in Canadian Journal of Chemistry in 1988.Quality Control of 3-Methyl-4-nitro-1H-pyrazole This article mentions the following:
Carbon-13 NMR spectroscopy in the solid state (cross polarization/magic angle spinning technique) is a very suitable method for studying the annular tautomerism of pyrazoles. In all the compounds studied, the tautomerism is frozen and the signals are well resolved except for 3,5-dimethyl-4-nitropyrazole, which shows broad signals. In the case of 4-substituted derivatives of 3(5)-methylpyrazoles, the tautomer present in the solid state is a 4-X-5 methylpyrazole. 3-Phenyl-5-methylpyrazole (4H or 4-methyl) is favored over the 3-methyl-5-phenyl-tautomer. In the experiment, the researchers used many compounds, for example, 3-Methyl-4-nitro-1H-pyrazole (cas: 5334-39-4Quality Control of 3-Methyl-4-nitro-1H-pyrazole).
3-Methyl-4-nitro-1H-pyrazole (cas: 5334-39-4) belongs to pyrazole derivatives. Pyrazole has two ring nitrogen atoms in which N1 is pyrrolic and N2 is pyridine-like. The N1 nitrogen is not reactive but is deprotonated in the presence of a base-forming anion. Protonation of pyrazole in strong acid leads to pyrazolium cations, which undergo electrophilic substitution preferentially at C3 rather than C4. The pyrazole anion is not reactive toward nucleophiles but is mostly reactive to electrophiles.Quality Control of 3-Methyl-4-nitro-1H-pyrazole
Referemce:
Pyrazole – Wikipedia,
Pyrazoles – an overview | ScienceDirect Topics