In-plane distortions

Fig. 8. Lattice distortions in a graphite sheet. For an in-plane distortion (left), the bond denoted by a thin line becomes shorter and that denoted by a thick line becomes longer, leading to a unit cell three times as large as the original. For an out-of-plane distortion (right), an atom denoted by a black dot is shifted down and that denoted by a white circle moves up.

A detailed analysis of Ni11 complexes with mew-substituted porphyrins bearing zero, one, two, or four /-butyl groups revealed that both the out-of-plane and in-plane distortion depend on the perturbation symmetry of the peripheral substituents (number and position of substitutents), and their orientation.1775 These results have implications for understanding the role of nonplanar distortions in the function of metalloproteins containing nonplanar porphyrins.1776... 

Fig. 5 on the previous page shows that the a Xn orbital pair seems to have suffered less in-plane distortion than its all-er counterparts in the same configuration. This supports the idea of a subdivision of roles within the configuration, with all-er orbitals providing most in-plane correlation, while the (o ln) pair provides very little of that, but all of the across-the-plane correlation (the plane referred to here is of course that of the nuclei). 

Pt(lll) 2C8H6+4CO (2 /3x4) rect Benzene ring parallel to surface over bridge sites, 2.10 A above surface, with two benzenes and four CO s per unit cell. CO also over bridge sites, 1.45 A above the metal surface. Benzene ring is expanded with small in-plane distortions consistent with local symmetry. LEED/10/... 

The pattern of electron densities in Figure 2 leaves no doubt that the 3e orbitals are C-C bonding whilst the le" are C-H bonding, the density lying out of the plane of the carbon atoms. Therefore it is to be expected that the orbitals labelled 3e are going to be much more susceptible to in-plane distortions such as depicted in Figure 8 than are those labelled le", explaining why the results of the dynamic Jahn-Teller effect are more evident in the 3e than in the le" case. 

To clarify this in more detail, the fundamental vibronic excitations of the DIP molecules were calculated from X-ray diffraction analyses as a function of temperature. Affecting the in-plane distortion of the orbital overlap. Figure 25.13 shows the temperature evolution of the librations around the principal molecular axes. 

Apart from in-plane distortions, bridgehead olefins of type 44 (Table 4) show torsion and oop bending. Typical examples and the precursors from which they are prepared are given in Scheme 7. 

J(13C, H) = 151.9 Hz) is compatible with hybridization at the =CH2 carbon atom which is unaffected by the in-plane distortion at the substituted C atom. 

The rather low frequencies for C=C bond stretching in the Bredt-olefins 69, 176,258, and 259 may be an indication of reduced 7t-bond order (96). Whereas the in-plane distortions of the trisubstituted olefins 257a and 257b hardly affect... 

It was mentioned earlier that the strain of a molecule is distributed over various degrees of freedom. Nevertheless, it is possible to distinguish olefins with preferential if not exclusive in-plane distortions from those with out-of-plane bending and torsional deformations. 

Benzene ring is expanded with small in-plane distortions consistent with local symmetry. 

In-plane distortion. In-plane distortion occurs in alkylaromatic hydrocarbons like those listed in Table 4, in the order of increasing in-plane strain, along with their maximum absorptivities. The absorptivity of the moderately strained (tetrachlorobenzo)cyclopentene (e = 235) is larger than that of the weakly strained (tetrachlorobenzo)cyclopentene (e = 450), as expected (Bal-lester and Riera, 1964a). It is most remarkable that the saturation effect in such in-plane distorted benzenes is non-existent, since the square law becomes applicable. 

Fig. 6.1 The Mexican hat potential-energy surface of the fi x e linear JT problem. The nuclear displacement coordinates are the tetragonal elongation, Qe, and the orthorhombic in-plane distortion,...

A direct relation between the first hyperpolarizability, of noncentrosy mmetric molecular structures and the centrosym-metricity content, 5(i), of such structures was shown for the first time in Ref. 5. For a series of systematic, in-plane distortions (stretch, pull, shift, and squish deformations) of the model non-linear optics chromophore benzene, a monotonic relationship between calculated values of f and 5(i) was found. The result suggests that the dominant variation in the hyperpolariz-ability for these structures arises from the change in oscillator strength. 

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