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.

中文翻译：

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OH自由基对1,3,5-三恶烷和1,4-二恶烷的吸氢反应动力学的理论研究

已对 1,3,5-三恶烷和 1,4-二恶烷环醚与 OH 自由基的双分子吸氢反应动力学进行了理论研究。考虑了从 1,3,5-三恶烷和 1,4-二恶烷的轴向和赤道位置提取氢。使用密度泛函理论在 M06-2X 水平上使用密度泛函理论进行了结构优化以及所有静止点（包括反应物、氢键配合物、过渡态和产物）的能量、振动频率和转动惯量的计算。 MG3S 基组。优化点的单点能量计算是在 CBS-QB3 级别获得的。计算表明，由于 OH 自由基和环醚的氧原子之间的氢键，标题反应通过相对强的氢键配合物进行。两个过渡态模型（内部紧密过渡态和外部松散过渡态）被用来计算吸氢率系数。出于比较的目的，还使用考虑紧密过渡状态的传统过渡状态理论计算了速率系数。发现当反应通过相对能量高于反应物的内部过渡态进行时，计算的速率系数被传统的过渡态理论低估了。两个过渡态模型（内部紧密过渡态和外部松散过渡态）被用来计算吸氢率系数。出于比较的目的，还使用考虑紧密过渡状态的传统过渡状态理论计算了速率系数。发现当反应通过相对能量高于反应物的内部过渡态进行时，计算的速率系数被传统的过渡态理论低估了。两个过渡态模型（内部紧密过渡态和外部松散过渡态）被用来计算吸氢率系数。出于比较的目的，还使用考虑紧密过渡状态的传统过渡状态理论计算了速率系数。发现当反应通过相对能量高于反应物的内部过渡态进行时，计算的速率系数被传统的过渡态理论低估了。