Solid-State Structure and Tautomerism of 2-Aminotroponimines Studied by X-ray Crystallography and Multinuclear NMR Spectroscopy

• Published in: European journal of organic chemistry 2004-11, Vol.2004 (21), p.4452-4466
• Main Authors: Claramunt, Rosa M., Sanz, Dionisia, Pérez-Torralba, Marta, Pinilla, Elena, Torres, M. Rosario, Elguero, José
• Format: Article
• Language: English
• Subjects: Aminotropones; Aminotroponimines; Density functional calculations; Hydrogen bond; NMR spectroscopy; Tautomerism; X-ray diffraction
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200400389

Structural studies in the solid state by X‐ray crystallography and by 13C and 15N CPMAS NMR spectroscopy carried out on a series of 2‐aminotroponimine derivatives 2−5 has allowed to establish the existence of hydrogen bonding and to determine the most stable tautomer. Almost all the structures reflect the classical double‐well potential function for the N−H···N hydrogen bonds. Only in the case of the compound N‐(pyrrol‐1‐yl)‐2‐(pyrrol‐1‐ylamino)troponimine (5) the crystal structure shows two independent molecules, one with a classical hydrogen bond and another with either a single‐well or a low‐barrier hydrogen bond. The structure of this compound is discussed with the use of the solid‐state NMR spectroscopic data. 2‐Aminotropones, as intermediates to the 2‐aminotroponimines, show the oxo‐tautomer as the stable form. B3LYP/6‐31G* calculations are used to rationalise the experimental results. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)