Fernández-González Miguel Ángel, Frutos Luis Manuel
Departamento de Química Analítica, Química Física e Ingeniería Química, Universidad de Alcalá, E- 28871, Alcalá de Henares, Madrid, Spain.
Departamento de Química Analítica, Química Física e Ingeniería Química, and Instituto de Investigación Química "Andrés M. del Río" (IQAR), Universidad de Alcalá, E- 28871, Alcalá de Henares, Madrid, Spain.
J Chem Phys. 2021 Jun 14;154(22):224106. doi: 10.1063/5.0052836.
Controlling the thermochemistry and kinetics of chemical reactions is a central problem in chemistry. Among factors permitting this control, the substituent effect constitutes a remarkable example. Here, we develop a model accounting for the effect of a substituent on the potential energy surface of the substrate (i.e., substituted molecule). We show that substituents affect the substrate by exerting forces on the nuclei. These substituent-induced forces are able to develop a work when the molecule follows a given reaction path. By applying a simple mechanical model, it becomes possible to quantify this work, which corresponds to the energy variation due to the effect of the substituent along a specific pathway. Our model accounts for the Hammett equation as a particular case, providing the first non-empirical scale for the σ and ρ constants, which, in the developed model, are related to the forces exerted by the substituents (σ) and the reaction path length (ρ), giving their product (σ · ρ) the well-known variation on the reaction energy due to the substituent.
控制化学反应的热化学和动力学是化学中的核心问题。在能够实现这种控制的诸多因素中，取代基效应就是一个显著的例子。在此，我们构建了一个模型，用于解释取代基对底物（即被取代分子）势能面的影响。我们表明，取代基通过对原子核施加力来影响底物。当分子沿着给定的反应路径进行时，这些由取代基诱导的力能够产生功。通过应用一个简单的力学模型，就有可能对这个功进行量化，它对应于沿着特定路径由于取代基效应而产生的能量变化。我们的模型将哈米特方程作为一个特殊情况包含在内，为σ和ρ常数提供了首个非经验标度，在我们所构建的模型中，它们分别与取代基施加的力（σ）和反应路径长度（ρ）相关，其乘积（σ·ρ）即为因取代基而导致的反应能量的著名变化。
