Double bond, electronic structure strength

Carbon dioxide is a linear molecule with equivalent C O distances of 1.16 A (Vol pin and Kolomnikov, 1973). The bond strength in C02 is measured to be D= 127.1 kcal mol 1, relatively weak compared with the CO bond in carbon monoxide (D = 258.2 kcal mol ) (Bard et al., 1985 Latimer, 1952 Weast, 1978). Resonance structures of the C02 molecule as illustrated in Figure 3.2 show that its chemical reactivity is associated either with the presence of carbon oxygen double bonds and lone-paired electrons on the oxygen atoms or with the electrophilic carbon atom. The quantitative mole-... 

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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