IUCr journals

meso-4,4′-Difluoro-2,2′-{[(3aR,7aS)-2,3,3a,4,5,6,7,7a-octahydro-1H-1,3-benzimidazole-1,3-diyl]-bis(methylene)}diphenol

Acta Cryst. (2013). E69, o217 (http://doi.org/ksk)

[Ellipsoid plot] A perspective view of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are drawn as dashed lines.

In 1,1-diamines the conformations are strongly disfavored if the unshared electron pairs on nonadjacent N atoms are parallel or syn-axial. The consequences are seen in the preferred conformation of certain heterocyclic rings. Eliel proposed to call this phenomenon the 'rabbit-ear effect'. The crystal structure of the title compound established the existence of a 'rabbit-ear effect' in the N-C-N aminal motif in which the lone pairs of the N atoms are located in syn disposition. The title compound is a good model to study intracyclic stereoelectronic effects.

A. Rivera, D. Quiroga, J. Ríos-Motta, M. Kuceraková and M. Dusek