Instituto de Química, Unversidad Nacional Autónoma de México, México DF, México.
J Phys Chem A. 2011 Nov 17;115(45):12924-32. doi: 10.1021/jp204030e. Epub 2011 Sep 16.
Theoretical studies about reaction mechanisms are usually limited to the determination of the energetic paths that connect reactants, transition states, and products. Recently, our group proposed the structural evolution, which has provided insights about the molecular structure changes occurring along a reaction path. Structural evolution may be defined as the development of a chemical reaction system across the partitioning of the nuclear configuration space into a finite number of structural regions defined on account of the topology of a scalar field, e.g., the electron density. In this paper, we present a tool to investigate within the framework of the Quantum Theory of Atoms in Molecules the evolvement of the Valence Shell Charge Concentration, the VSCC evolution, which is the description of the changes of electron density concentrations and depletions around the bonding area of an atom. The VSCC evolution provides supplementary information to the structural evolution because it allows the analysis of valence shells within a structural region, i.e., a subset of R(Q) with the same connectivity among the atoms forming a molecule. This new approach constitutes also a complement to the Valence-Shell Electron Pair Repulsion (VSEPR) model because it gives an account of the adjustments of electron pairs in the valence shell of an atom across a chemical reaction. The insertion reaction in the hydroformylation reaction of ethylene, the reduction of cyclohexanone with lithium aluminum hydride, the oxidation of methanol with chlorochromate, and the bimolecular nucleophilic substitution of CH(3)F with F(-) are used as representatives examples of the application of the VSCC evolution. Overall, this paper shows how the VSCC evolution through an analysis of the modifications of local charge concentrations and depletions in individual steps of a chemical reaction gives new insights about these processes.
理论研究反应机制通常仅限于确定连接反应物、过渡态和产物的能量路径。最近，我们小组提出了结构演化，它提供了关于沿反应路径发生的分子结构变化的见解。结构演化可以定义为化学反应系统在核构形空间的划分上的发展，通过拓扑学的标量场，例如电子密度，将其划分为有限数量的结构区域。在本文中，我们提出了一种工具，用于在原子分子量子理论的框架内研究价壳电荷浓度的演化，即 VSCC 演化，这是对原子键合区域周围电子密度浓度和耗尽变化的描述。VSCC 演化提供了结构演化的补充信息，因为它允许在一个结构区域内分析价壳，即 R(Q)的一个子集，其中形成分子的原子之间具有相同的连接性。这种新方法也是对价层电子对排斥 (VSEPR) 模型的补充，因为它说明了在化学反应中原子价壳中电子对的调整。乙烯的氢甲酰化反应中的插入反应、环己酮与氢化铝锂的还原反应、甲醇与重铬酸氯的氧化反应以及 CH(3)F 与 F(-)的双分子亲核取代反应被用作应用 VSCC 演化的代表性示例。总体而言，本文展示了通过分析化学反应中各个步骤中局部电荷浓度和耗尽的变化，VSCC 演化如何提供关于这些过程的新见解。
