Benzene buckling

Benzene-ring orientation 100 Boundary layer 151 Broad line NMR 197 Buckling of fibrils 140... 

The results of a two-dimensional X-ray analysis of the 12-molecule crystal structure (McIntosh et al., 1954) reveal that for the molecules in the special positions, the separation between overcrowded carbon atoms is 2 9 A and for the molecules in general positions, 3-1 A. The experimental accuracy is between 0T and 0-2 A, and the mean value of these separations, 3-0 A, may be taken as indicating the magnitude of the displacement. This distortion is achieved with no major changes in bond angles or severe buckling of any benzene ring (Fig. 18). The... 

A particularly interesting dianion is that derived from bis(cyclo-octatetraeno[l,2 4,5]benzene [304]. Possible structures are (XLVII), which contains a 14 r-electron periphery bridged by a cycloocta-tetraene ring which takes up a relatively strain-free buckled shape, or structure (XLVIII], which takes the form of a peripherally delocalised dlanion made up of 20 r-electrons with strain introduced... 

The center of the benzene molecule, which defines the adsorption site or axis, lies over an fcc-hollow site (indicated by the heading of Table 3). The height of the C atoms of the benzene, above the first ring of Pd atoms around the fcc-hollow site in the top metal layer, is given as doi = 2.16 0.05 A. The second shell of Pd atoms around that site in the top metal layer is buckled into the substrate by bib = 2.2 2.2 %, relative to the first shell, for which (by definition) bia = 0.0 ( 2.2) %, while its shell radius is (perhaps) expanded by Arib = 0.8 7.0 % relative to bulk positions. No rotations ais are noted, and no information about the second metal layer 1 = 2 is given, other than its spacing of Adn = 2.6 2.2 A, measured relative to the first shell of Pd atoms in the first Pd layer the second Pd layer is thus, in this example, assumed to be internally unrelaxed, i.e. not to be buckled, expanded laterally or rotated. 

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