Quantum Chemical Study of the Initial Step of Ozone Addition to the Double Bond of Ethylene

Abstract

The mechanisms of the initial step in chemical reaction between ozone and ethylene were studied by multireference perturbation theory methods (MRMP2, CASPT2, NEVPT2, and CIPT2) and density functional theory (OPW91, OPBE, and OTPSS functionals). Two possible reaction channels were considered: concerted addition through the symmetric transition state (Criegee mechanism) and stepwise addition by the biradical mechanism (DeMore mechanism). Predicted structures of intermediates and transition states, the energies of elementary steps, and activation barriers were reported. For the rate-determining steps of both mechanisms, the full geometry optimization of stationary points was performed at the CASPT2/cc-pVDZ theory level, and the potential energy surface profiles were constructed at the MRMP2/cc-pVTZ, NEVPT2/cc-pVDZ, and CIPT2/cc-pVDZ theory levels. The rate constants and their ratio for reaction channels calculated for both mechanisms demonstrate that the Criegee mechanism is predominant for this reaction. These results are also in agreement with the experimental data and previous computational results. The structure of DeMore prereactive complex is reported here for the first time at the CCSD(T)/cc-pVTZ and CASPT2/cc-pVDZ levels. Relative stability of the complexes and activation energies were refined by single-point energy calculations at the CCSD(T)-F12/VTZ-F12 level. The IR shifts of ozone bands due to formation of complexes are presented and discussed.

Kinetics and mechanism of ozone addition to olefins and dienes

“…As distinct from the data presented in Table 3, the data listed in Table 4 take into account the TS degeneracy, and the calcu lated preexponential factors and rate constant values appearing there have already been multiplied by the corresponding coefficients. Note that the data for ethylene were reported tens of times, including in our publication [3]. Here, they are reported for two rea sons, firstly for comparing ethylene with other objects and, secondly, for comparing the calculated data to experimental data with account taken of the TS degeneracy (see above), which was not done earlier.…”

“…In this sense, butadiene is not an exception, so initially it is necessary to find the TS's with which the reaction is energetically most favorable. For molecules with an unconjugated double bond, this was done in earlier works [3,[10][11][12]. For butadiene, we carried out the simplest calculation of total electronic energy for the possible TS's ( Table 1, Figs.…”

“…At its early stages, the reaction may take place both via con certed 1,3 cycloaddition (Criegee mechanism) [1], passing through a symmetric transition state (TS1), and via nonconcerted addition (DeMore mechanism) [2], passing through a biradical transition state (TS2). The competition between these pathways was consid ered in an earlier work [3]. Because of the high exother micity of the process, the resulting primary products undergo further conversion to yield a wide variety of final products.…”

Quantum chemical and master equation study of OH + CH2O → H2O + CHO reaction rates in supercritical CO2 environment

“…Another advantage of oxy‐combustion is the ability of CO 2 to form a supercritical fluid with a high thermal expansion coefficient, increasing the efficiency of the turbine . Combustion kinetics may alter at large concentrations of CO 2 , and theoretical chemistry can assist in studying these effects . In the first paper of this series, we investigated the effect of CO 2 on the CO + OH reactive system and found a lower activation energy pathway in which CO 2 participated covalently .…”

“…3,4 Combustion kinetics may alter at large concentrations of CO 2 , and theoretical chemistry can assist in studying these effects. [5][6][7][8] In the first paper of this series, we investigated the effect of CO 2 on the CO + OH reactive system and found a lower activation energy pathway in which CO 2 participated covalently. 9 In the following papers, we reported lowering of the activation barrier of seven other combustion reactions via van der Waals (vdW) interactions with CO 2 .…”