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

AutorCabildo, Pilar; Claramunt, Rosa M.; Zúñiga, F. J.; Alkorta, Ibon ; Elguero, José
Fecha de publicación2015
EditorWalter de Gruyter
CitaciónZeitschrift fur Kristallographie - Crystalline Materials 230: 427-438 (2015)
ResumenThe 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 = C<inf>4</inf>H<inf>9</inf>, CH<inf>2</inf>C<inf>6</inf>H<inf>5</inf> and C<inf>6</inf>H<inf>5</inf>), but disagreements are found for R = H, CH<inf>3</inf>.
Versión del editorhttp://dx.doi.org/10.1515/zkri-2015-0004
Identificadoresdoi: 10.1515/zkri-2015-0004
issn: 2196-7105
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