Single bond, electronic structure strength

Single bond, electronic structure of, 14 length of, 14 see also Alkane strength of, 14 Skeletal structure, 23... 

In summary, we emphasize that homoaromatic stabilization appears to be more important for radical cations than for their neutral diamagnetic precursors. There are several reasons why radical cations may assume cyclic conjugated structures with 4n + 17i-electrons, one electron shy of the magic 4n + 2 7i-electrons which achieve aromaticity, when the parent molecules opt for a less delocalized nonaromatic structure. The principal cause might lie in the strength of the carbon-carbon single bond, which generally disfavors biradical or zwitterionic... 

With O2, we really see the power of MO theory compared to theories based on localized orbitals. For years, it seemed impossible to reconcile bonding theories with the bond strength and magnetic behavior of O2. On the one hand, the data show a double-bonded molecule that is paramagnetic. On the other hand, we can write two possible Lewis structures for O2, but neither gives such a molecule. One has a double bond and all electrons paired, the other a single bond and two electrons unpaired ... 

Figure 5. The Fries model of the electronic structure of Cjo- The HUckel eigenvalues are plotted as a function of r, the relative size of the resonance integral for the "single bonds to that of the formal double bonds of the Fries structure. The limiting case on the RHS is the neutral molecule with all bonds of equal strength, showing that all bonding levels of C o derive from local bonding orbitals associated with the formal double bonds. The degeneracy of the levels is indicated by the symmetry label at the RHS.

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