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Formation of a covalent bond is not necessarily associated with an increase in electron density in the bonding region. This can be established by analysis of the single electron density distributions ρ(r) with the aid of the assigned Laplace field ▽2ρ(r). For “bonds without bonding electron density ρ(r)”, it is decisive that the density ρ(r) actually present in the region between the atoms results in a decrease in the local energy density and, hence, produces a stabilizing effect.

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A detailed kinetic analysis of the complex reaction systems arising from the ozonolysis of C2H4 and (CH3)2CC(CH3)2 (TME), respectively, is carried out, using master equations and statistical rate theory. The thermochemical as well as the molecular data required are obtained from CCSD(T)/TZ2P and B3LYP/DZP calculations. It is shown that the primary ozonides are not collisionally stabilized under atmospheric conditions. In the reaction sequence for O3 + TME, the same is true for CH2C(CH3)OOH formed from (CH3)2COO, which completely dissociates to give OH radicals. However, in this system, a pressure dependence is predicted for the relative branching fractions of the reactions of the Criegee intermediate. Under atmospheric conditions, for both examples, the product yields obtained are in reasonable agreement with experimental results.