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Licensed Unlicensed Requires Authentication Published by De Gruyter (O) March 28, 2015

Crystal and molecular structures of two 1H-2-substituted benzimidazoles

  • Pilar Cabildo , Rosa M. Claramunt , Fco. Javier Zuñiga EMAIL logo , Ibon Alkorta and Jose Elguero

Abstract

The X-ray molecular structure of two benzimidazoles unsubstituted on the nitrogen atoms (2-ethyl-1H-benzimidazole and 2-propyl-1H-benzimidazole) has been determined and analysed in the context of crystallographic and solid-state NMR data of seven substituted benzimidazoles. The first compound presents polymorphism, and two polymorphs [forms 3a and 3c] were obtained from different solutions of dichloromethane/hexane. Polymorph (3a) contains two independent molecules differing in the conformation of the ethyl group. Polymorph (3c) contains only one molecule in the asymmetric unit, with similar configuration as the ordered molecule of polymorph (3a). Another polymorphic form (3b) is obtained by cooling form (3a) below 179 K. The transition is related to an order-disorder process and involves a change in the hydrogen-bonding scheme. The second compound (4) presents enantiomorphism and its asymmetric unit contains four independent molecules that differ in the conformation of the 2-propyl group. For form (3a), the splitting of NMR signals is almost perfectly consistent with the features of the crystal structure, whereas not splitting is observed for compound (4). Agreements between NMR and X-ray crystallography techniques are also observed in other simple 2-R-1H-benzimidazoles (R = C4H9, CH2C6H5 and C6H5), but disagreements are found for R = H, CH3.


Corresponding author: Fco. Javier Zuñiga, Fac. Ciencia y Tecnología, Dpto. Física Materia Condensada, Universidad del Pais Vasco, APDO. 644, 48080 Bilbao, Spain, E-mail:

Acknowledgments

Authors thanks to Prof. T. Breczewski for helping in DSC measurements. This work has been financed by Ministerio de Ciencia e Innovación (CTQ2010-16122) and Ministerio de Economía y Competitividad of Spain (CTQ2012-35513-C02-02) and Comunidad Autónoma de Madrid (Project MADRISOLAR2, ref. S2009/PPQ-1533). This work was also supported by the Basque Government (project IT779-13).

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Supplemental Material:

The online version of this article (DOI: 10.1515/zkri-2015-0004) offers supplementary material, available to authorised users.


Received: 2014-11-19
Accepted: 2015-2-23
Published Online: 2015-3-28
Published in Print: 2015-6-1

©2015 by De Gruyter

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