8- direction, coplanar within

In a similar way Kekule s theory of the benzene structure has been very completely established by the whole development of aromatic chemistry. The direct physical verification of the presumably planar arrangement was in this case more delayed. The crystal structure of graphite was examined almost as soon as that of diamond, but the early results were inconclusive. The structure is not determined by the symmetry alone, and the later detailed investigation by Bernal (1924) showed that the carbon atoms in the hexagonal net must be coplanar to within at least 0-38 A. Later work by Ott (1928) narrowed this limit still further. Although it is generally assumed that the atoms are coplanar, the exactness with which this can be established depends on... 

A single crystal X-ray diffraction analysis has been carried out on the bromo-substituted isocorrole derivative 2.269. This analysis revealed a somewhat non-planar macrocyclic structure (Figure 2.2.2). The non-planarity in 2.269 was presumed to arise primarily as the result of NH steric interactions present within the core of the macrocycle. As a consequence of these interactions, the two pyrroles of the dipyrrylmethene-like end of the macrocycle each twist by 23° in opposite directions out of the mean macrocyclic plane. This out-of-plane rotation of two pyrrole rings is in contrast to that observed in a typical corrole structure. In this latter case, three of the pyrrole rings are nearly coplanar, and one of the pyrroles is rotated out of plane but only by 8-10°... 

Fig. 1 The spatial arrangement of the particles within a port Both up and down contain the same arrangement of four non-coplanar particles except that they face opposite directions...

The molecular structure of Sc2-naph (Fig. 11) was reminiscent of previously reported yttrium naphthalene complexes (Fryzuk et al., 2000). The naphthalene is distorted from planarity with C2/C3 and C2A/C3A bending in opposite directions from the plane composed of the other six carbon atoms (ca. 20° torsion angle). The C-C bonds within the naphthalene are best described as two isolated double bonds (C2=C3 and C2A=C3A), with short distances averaging 1.37 A, and a 6C, 871-electron system for the six coplanar center carbon atoms. Each scandium ion binds to Cl through C4 (or CIA through C4A) with similar distances averaging 2.51 A. These features are also reminiscent of those of the lithium naphthalene dianion [Li(TMEDA)]2(p-ri ri -CioH8) (TMEDA = tetramethylethylenediamine) (Melero et al., 2009). 

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