Tautomerism and reactivity in heterocyclic N-Oxides. A spectrocopic and theoretical study of benzimidazole N-Oxide derivatives (N-Hydroxybenzimidazoles.

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Tautomerism and reactivity in heterocyclic N-Oxides. A spectrocopic and theoretical study of benzimidazole N-Oxide derivatives (N-Hydroxybenzimidazoles.

Tema

BENZIMIDAZOL
BIBLIOGRAFIA NACIONAL QUIMICA
2004

Abstract

The tautomeric forms of benzimidazole N-oxide derivatives in solution were studied using nuclear magnetic resonance (NMR) techniques. Further insight into the molecular structures was provided by theoretical calculations using density functional theory (DFT). In the gas phase the N-hydroxy tautomer was more stable than the N-oxide, whereas in solution the stabilization of one form or the other depended on hydrogen bond formation involving the N-hydroxy/N-oxide moiety. Derivative 4 (n-butyl-5-nitrobenzimidazole-2-carboxamide 3-oxide), having a 2-carboxamide moiety, was the only compound studied present as a mixture of tautomers, the N-oxide being the predominant one. This was assigned to the formation of an internal hydrogen bond between the N-oxide group and the amide hydrogen atom. The tautomeric form present in the solid state was studied for derivative 1 (ethyl-5-nitrobenzimidazole-2-carboxylate 3-oxide) and was conclusively assigned by X-ray diffraction techniques to the N-hydroxy tautomer. In the crystal a strong O-HâââN intermolecular bond gives rise to supramolecular polymeric chains in the lattice. This strong interaction was also seen in the infrared spectrum and was assigned to two broad bands at 2367 and 2526 cm-1. The vibrational spectrum was satisfactorily described by DFT calculations and an example of this is the prediction of the band corresponding to the N-O stretching (N-oxide) just 1% lower than the experimental value. Uncorrelated calculations (HF) were not able to give an unambiguous assignment of this band. The reaction of derivative 1 against different kinds of electrophiles, hard and soft, led only to O-substituted products. This result was explained in terms of the HSAB theory using a local-global approach.

Autor

Boiani Santurio, Mariana
Cerecetto, Hugo
González, Mercedes.
Piro, Oscar E
Castellano, Eduardo E

Fuente

Journal of Physical Chemistry A v. 108, no. 51, 2004. -- p. 11241-11248

Editor

American Chemical Society

Fecha

2004

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Artículo

Identificador

DOI: 10.1021/jp046826v

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PDF
Fecha de agregación
April 15, 2015
Colección
Bibliografía Nacional Química
Tipo de Elemento
Document
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Citación
Boiani Santurio, Mariana, “Tautomerism and reactivity in heterocyclic N-Oxides. A spectrocopic and theoretical study of benzimidazole N-Oxide derivatives (N-Hydroxybenzimidazoles.,” RIQUIM - Repositorio Institucional de la Facultad de Química - UdelaR, accessed November 22, 2019, http://riquim.fq.edu.uy/items/show/2753.
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