Influence of Substituents on the Gas‐Phase Ozonolysis of Ethene: A Theoretical Study

The effects of electron-donating group (EDG) and electron-withdrawing group (EWG) substitution on the mechanism and kinetics of ozonolysis of ethene are studied in the present work. Quantum chemical methods and transition state theory are employed to understand the mechanistic and kinetic features of the substitution effects. The results show that the substitution of EDGs increases the reaction rate by lowering the activation free energy, whereas, the substitution of EWGs increases the activation free energy, thus slowing the reaction. The kinetics of primary ozonide (PO) formation are found to be influenced by the electron density around the CC bond. The dissociation of PO formed from monosubstituted ethene and geminal-substituted ethenes leads to the formation of the unsubstituted Criegee intermediate (CI), and for cis- and trans-substituted ethenes, the dissociation of PO leads to the formation of CI with EDG. The modified Bell-Evans-Polanyi principle, which includes the energy of the highest occupied molecular orbital of the reactant, reliably predicts the activation free energy with high correlation (R² = 0.98) and minimal error. The above findings will contribute to the development of more accurate atmospheric chemistry models for the prediction of kinetics of ozonolysis reactions.