This study has examined the relative energetics of nine stationary points associated with the three different radical isomers generated by removing a H atom from ethanol at the O atom (ethoxy, CH₃CH₂O), the α C atom (CH₃CHOH), and the β C atom (CH₂CH₂OH). For the first time, CCSD(T) geometry optimizations and harmonic vibrational frequency computations with the cc-pVTZ and aug-cc-pVTZ basis sets have been carried out to characterize two unique minima for each isomer along with three transition state structures with C_s symmetry. Explicitly correlated CCSD(T) computations were also performed to estimate the relative energetics of these nine stationary points near the complete basis set limit. These benchmark results were used to assess the performance of various density functional theory (DFT) and wave function theory methods, and they will help guide method selection for future studies of alcohols and their radicals. The structures generated by abstracting H from the α C atom have significantly lower electronic energies (by at least 7 kcal mol⁻¹) than the CH₃CH₂O and CH₂CH₂OH radicals. Although previously reported as a minimum on the ground-state surface, the ²A″ C_s structure of the ethoxy radical was found to be a transition state in this study with MP2, CCSD(T), and a number of DFT methods. An implicit solvation model used in conjunction with DFT and MP2 methods did not qualitatively change the relative energies of the isomers, but the results suggest that the local minima for the CH₃CHOH and CH₂CH₂OH radicals could become more energetically competitive in condensed phase environments, such as liquid water and ethanol.

中文翻译：

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乙醇脱氢产生的 CH3CH2O、CH3CHOH 和 CH2CH2OH 自由基产物的相对能量学

本研究检查了与通过从乙醇中的 O 原子（乙氧基，CH ₃ CH ₂ O）、α C 原子（CH ₃ CHOH）、和βC原子（CH ₂ CH ₂ OH）。首次使用 cc-pVTZ 和 aug-cc-pVTZ 基组进行 CCSD(T) 几何优化和谐波振动频率计算，以表征每个异构体的两个唯一最小值以及三个具有 C _{s 的}过渡态结构对称。还执行了显式相关的 CCSD(T) 计算，以估计这九个固定点在完整基组极限附近的相对能量。这些基准结果用于评估各种密度泛函理论 (DFT) 和波函数理论方法的性能，它们将有助于指导未来醇类及其自由基研究的方法选择。通过从α C 原子中提取H 产生的结构具有比CH ₃ CH ₂ O 和CH ₂ CH ₂ OH 自由基显着更低的电子能（至少7 kcal mol ^-1）。尽管先前报道为基态表面的最小值，但² A ″ C _s在本研究中，使用 MP2、CCSD(T) 和许多 DFT 方法发现乙氧基自由基的结构是过渡态。与 DFT 和 MP2 方法结合使用的隐式溶剂化模型没有定性地改变异构体的相对能量，但结果表明 CH ₃ CHOH 和 CH ₂ CH ₂ OH 自由基的局部最小值可以在凝聚态中变得更具能量竞争性。相环境，如液态水和乙醇。