Passos Maiara Oliveira, Lins Igor Araujo, Venâncio Mateus Fernandes, Alves Tiago Vinicius
Departamento de Físico-Química, Instituto de Química - Universidade Federal da Bahia, Rua Barão de Jeremoabo, 147, Salvador, Bahia, 40170-115, Brazil.
Phys Chem Chem Phys. 2021 Nov 17;23(44):25414-25423. doi: 10.1039/d1cp03981d.
Thermal rate coefficients for the hydrogen-abstraction reactions of 3-butenal by a hydrogen atom were obtained applying multipath canonical variational theory with small-curvature tunneling (MP-CVT/SCT). Torsional anharmonicity due to the hindered rotors was taken into account by calculating the rovibrational partition function using the extended two-dimensional torsional (E2DT) method. For comparison, rovibrational partition functions were also estimated using the multistructural method with torsional anharmonicity based on a coupled torsional potential (MS-T(C)). By contrast, with ()-2-butenal reactions, the abstraction reactions of 3-butenal proceed five reaction channels (R1)-(R5). In a conformational search, 45 distinguishable structures of transition states were found, including enantiomers, which were separated into six conformational reaction channels (CRCs). The individual reactive paths were constructed, the recrossing and semiclassical transmission coefficients estimated, and the multipath rate constants were obtained. High torsional barriers between the wells of CRC2/CRC6 indicate a harmonic behavior. Consequently, a difference between the torsional anharmonicity of 3-butenal and the transition states is responsible for the increase in the thermal rate constants for channel (R2). Analysis of the contributions of each conformer of the transition state shows an important contribution of the high-energy rotamers in the total flux of (R1)-(R5). After fitting the rate constants in a four-parameter equation, the activation energy estimation showed a strong temperature dependence.
采用小曲率隧道效应多路径正则变分理论（MP-CVT/SCT）获得了氢原子与3-丁烯醛发生氢提取反应的热速率系数。通过使用扩展二维扭转（E2DT）方法计算振转配分函数，考虑了受阻转子引起的扭转非谐性。为作比较，还基于耦合扭转势使用具有扭转非谐性的多结构方法（MS-T(C)）估算了振转配分函数。相比之下，对于（±）-2-丁烯醛反应，3-丁烯醛的提取反应通过五个反应通道（R1）-（R5）进行。在构象搜索中，发现了45种可区分的过渡态结构，包括对映体，它们被分为六个构象反应通道（CRC）。构建了各个反应路径，估算了再交叉和半经典透射系数，并获得了多路径速率常数。CRC2/CRC6阱之间的高扭转势垒表明存在谐波行为。因此，3-丁烯醛与过渡态的扭转非谐性差异导致通道（R2）的热速率常数增加。对过渡态各构象贡献的分析表明，高能旋转异构体在（R1）-（R5）的总通量中起重要作用。在将速率常数拟合到四参数方程后，活化能估算显示出强烈的温度依赖性。
