Theoretical studies on the kinetics of the hydrogen-abstraction reactions from 1,3,5-trioxane and 1,4-dioxane by OH radicals

Abstract

Theoretical investigations have been performed on the kinetics of bimolecular hydrogen-abstraction reactions of 1,3,5-trioxane and 1,4-dioxane cyclic ethers with OH radicals. Hydrogen abstraction from both axial and equatorial positions of 1,3,5-trioxane and 1,4-dioxane was considered. Optimization of the structures, and the calculation of energies, vibrational frequencies and moments of inertia for all the stationary points including reactants, hydrogen-bonded complexes, transition states and products were carried out using density functional theory at the M06-2X level together with the MG3S basis set. Single-point energy calculations on the optimized points were obtained at the CBS-QB3 level. The calculations show that the title reactions proceed through relatively strong hydrogen-bonded complexes due to the hydrogen bonding between the OH radicals and the oxygen atoms of the cyclic ethers. A two-transition state model (an inner tight transition state and an outer loose transition state) was employed to compute the hydrogen-abstraction rate coefficients. The rate coefficients were also computed using conventional transition state theory considering a tight transition state for the purpose of comparison. It was found that when the reactions proceed via inner transition states with relative energies higher than the reactants, the computed rate coefficients are underestimated by conventional transition state theory.

Photooxidation Reactions of Ethyl 2-Methylpropionate (E2MP) and Ethyl 2,2-Dimethylpropionate (E22DMP) Initiated by OH Radicals: An Experimental and Computational Study

“…A meta-hybrid functional, M06-2X (with 54% HF exchange) − coupled with Pople’s basis set 6-311++G­(2d,2p) (MG3S) , was used for the optimization of the reactants (E2MP and E22DMP), transition states (TSs) and products (P i ). The use of the M062X method in combination with the MG3S basis set is known to have the best performance, and it is selected for use for direct dynamics calculations. − Individually, both the M06-2X method as well as the MG3S basis set are known to be good for the computation of accurate barrier heights and thermodynamic parameters. Details of the computational methodology are specified in section of the Supporting Information.…”

Chemical kinetics of cyclic ethers in combustion

“…In the low-temperature oxidation regime below 900 Chakravarty and Fernandes [608] and Illés et al [607], from THP by Tran et al [196], from 1,4-dioxane and 1,3,5-trioxane by Saheb and Bahadori [609], and from lactones by Barnes et al. [604] and De Bruycker et al [259].…”