has been investigated by the B3LYP density functional theory (DFT) method, B2PLYP double hybrid method
based on DFT and the MP2 approximation, and CCSD coupled cluster method. Two possible butadiene and
olefin ozonolysis mechanisms are considered: concerted 1,3-cycloaddition, which yields a primary ozonide
(Criegee mechanism) and stepwise ozone addition via a biradical transition state (DeMore mechanism). The
geometries of the initial and transition states and the energies of the elementary steps of the reaction have been
determined. The geometric structures of the stationary states determining the rate constant of the reaction have
been completely optimized using the above methods and the aug-cc-pVDZ basis set. The rate constants for both
reaction pathways have been calculated. For butadiene, the contribution from nonconcerted addition can
reaches 25%. According to the MRMP2 method, the overall rate constant (which includes both reaction path-
ways) is 1778 L mol–1 s–1; according to B2PLYP, 1640 L mol–1 s–1; according to CCSD, 1424 L mol–1 s–1 (aug-
cc-pVDZ basis set). These results are in good agreement with experimental data (k = 3
103 L mol–1 s–1 and with earlier calculations. The data calculated for olefins are also in agreement with experimental data.