Molecular system homocyclic

We note that these differences are indicative of the effects of charge transfer (CT) in these systems. In Figure 4.2, we present the highest occupied molecular orbitals (HOMOs) for the above-mentioned molecular systems. For the homocyclic molecular systems CgHg and C4H4 (Figure 4.2a and b), we find that the nodal plane passes through the bonds and the molecular orbitals (MOs) are delocalized over aU the... 

Interestingly, the energy difference is smallest for S7O which as a heterocycle forms a crown-shaped eight-membered ring similar to and isoelec-tronic with the well known 8 structure of 04a symmetry. The transformation of the heterocycle S7O into the homocyclic isomer 7=0 was studied by the molecular dynamics/density functional method but the unrealistically high barrier of 5 eV calculated for this transformation indicates that the system was far from equilibrium during most of the simulation [66]. 

Many of the above-mentioned compounds have been first prepared or properly characterized after 1968. It therefore can be expected that new species of similar types will be synthesized in the near future. Their investigation by modern analytical techniques will finally help to elucidate the molecular structure of more complex systems such as amorphous, glassy, and liquid elemental selenium. In this context the already better understood homocyclic sulfur compounds and, in particular, the mixed species, the heterocyclic selenium sulfides (55), can serve as models to study the structural and chemical behavior of the selenium-selenium bond. 

In the crystalline state, the site symmetry is in general lower than the symmetry of the free molecule. The preferred lattice structures of sulfur homocycles are of the orthorhombic and monoclinic crystal systems. The molecular packing arrangements of the soKd allotropes are quite different In orthorhombic Si2, for example, the asymmetric unit is given by one quarter... 

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