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Molecules 2018, 23(1), 129; doi:10.3390/molecules23010129

On the Tautomerism of N-Substituted Pyrazolones: 1,2-Dihydro-3H-pyrazol-3-ones versus 1H-Pyrazol-3-ols

1
Department of Organic Chemistry, Kaunas University of Technology, Radvilėnų pl. 19, LT-50254 Kaunas, Lithuania
2
Institute of Synthetic Chemistry, Kaunas University of Technology, K. Baršausko g. 59, LT-51423 Kaunas, Lithuania
3
Institute of Organic Chemistry, Johannes Kepler University Linz, Altenberger Straße 69, A-4040 Linz, Austria
4
X-ray Structure Analysis Centre, Faculty of Chemistry, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria
5
Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
*
Authors to whom correspondence should be addressed.
Received: 27 November 2017 / Revised: 28 December 2017 / Accepted: 30 December 2017 / Published: 9 January 2018
(This article belongs to the Special Issue Pyrazole Derivatives)
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Abstract

The tautomerism of 1-phenyl-1,2-dihydro-3H-pyrazol-3-One was investigated. An X-ray crystal structure analysis exhibits dimers of 1-phenyl-1H-pyrazol-3-ol units. Comparison of NMR (nuclear magnetic resonance) spectra in liquid state (1H, 13C, 15N) with those of “fixed” derivatives, as well as with the corresponding solid state NMR spectra reveal this compound to exist predominantly as 1H-pyrazol-3-ol molecule pairs in nonpolar solvents like CDCl3 or C6D6, whereas in DMSO-d6 the corresponding monomers are at hand. Moreover, the NMR data of different related 1H-pyrazol-3-ol derivatives are presented. View Full-Text
Keywords: prototropic tautomerism; 1H-pyrazol-3-ol; 1,2-dihydro-3H-pyrazol-3-ones; NMR (1H; 13C; 15N); solid state NMR; X-ray structure analysis prototropic tautomerism; 1H-pyrazol-3-ol; 1,2-dihydro-3H-pyrazol-3-ones; NMR (1H; 13C; 15N); solid state NMR; X-ray structure analysis
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Arbačiauskienė, E.; Krikštolaitytė, S.; Mitrulevičienė, A.; Bieliauskas, A.; Martynaitis, V.; Bechmann, M.; Roller, A.; Šačkus, A.; Holzer, W. On the Tautomerism of N-Substituted Pyrazolones: 1,2-Dihydro-3H-pyrazol-3-ones versus 1H-Pyrazol-3-ols. Molecules 2018, 23, 129.

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