Structure of a 4-Nitroso-5-aminopyrazole and Its Salts:  Tautomerism, Protonation, and E/Z Isomerism

• Published in: Journal of organic chemistry Vol. 68; no. 23; pp. 8831 - 8837
• Main Authors: Holschbach, Marcus H, Sanz, Dionisia, Claramunt, Rosa M, Infantes, Lourdes, Motherwell, Sam, Raithby, Paul R, Jimeno, María Luisa, Herrero, David, Alkorta, Ibon, Jagerovic, Nadine, Elguero, José
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14-11-2003
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Organic chemistry; Preparations and properties; Nitroso compound; Chemical solution; Ethanol; Molecular structure; Nitrogen heterocycle; Solvatochromism; Oxime; NMR spectrometry; Tautomerism; Imine; Tautomer; X ray diffraction; Isomerism; Solid state; Methyl sulfoxide; Amine; Benzylic compound; Density functional method; Pyrazole derivatives; Protonation; Cations; Hydrogen bond; Methanol
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo034833u

The structures of 1-benzyl-4-nitroso-5-aminopyrazole (1) and its hydrochloride (1H + ) have been determined in the solid state and in solution in DMSO, methanol, and ethanol. The free base exists in solution as a mixture of amino/nitroso tautomers 2a and 2b rather than in the imino/oxime tautomers 3. The conjugated cation 1H + results from the protonation of the nitroso group. X-ray crystallography showed that both amino hydrogen atoms of 2a form NH···ON hydrogen bonds:  one is intramolecular, the other links adjacent molecules in an infinite chain.