Departament de Ciències Experimentals Universitat Jaume I, 12080 Castelló, Spain.
Chem Commun (Camb). 2016 Jul 7;52(53):8183-95. doi: 10.1039/c5cc09816e. Epub 2016 May 24.
Probing the electron density transfers during a chemical reaction can provide important insights, making possible to understand and control chemical reactions. This aim has required extensions of the relationships between the traditional chemical concepts and the quantum mechanical ones. The present work examines the detailed chemical insights that have been generated through 100 years of work worldwide on G. N. Lewis's ground breaking paper on The Atom and the Molecule (Lewis, G. N. The Atom and the Molecule, J. Am. Chem. Soc. 1916, 38, 762-785), with a focus on how the determination of reaction mechanisms can be reached applying the bonding evolution theory (BET), emphasizing how curly arrows meet electron density transfers in chemical reaction mechanisms and how the Lewis structure can be recovered. BET that combines the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT) provides a powerful tool providing insight into molecular mechanisms of chemical rearrangements. In agreement with physical laws and quantum theoretical insights, BET can be considered as an appropriate tool to tackle chemical reactivity with a wide range of possible applications. Likewise, the present approach retrieves the classical curly arrows used to describe the rearrangements of chemical bonds for a given reaction mechanism, providing detailed physical grounds for this type of representation. The ideas underlying the valence-shell-electron pair-repulsion (VSEPR) model applied to non-equilibrium geometries provide simple chemical explanations of density transfers. For a given geometry around a central atom, the arrangement of the electronic domain may comply or not with the VSEPR rules according with the valence shell population of the considered atom. A deformation yields arrangements which are either VSEPR defective (at least a domain is missing to match the VSEPR arrangement corresponding to the geometry of the ligands), VSEPR compliant or pseudo VSEPR when the position of bonding and non-bonding domains are interchanged. VSEPR defective arrangements increase the electrophilic character of the site whereas the VSEPR compliant arrangements anticipate the formation of a new covalent bond. The frequencies of the normal modes which account for the reaction coordinate provide additional information on the succession of the density transfers. This simple model is shown to yield results in very good agreement with those obtained by BET.
探究化学反应过程中的电子密度转移可以提供重要的见解，从而使人们有可能理解和控制化学反应。这一目标需要扩展传统化学概念与量子力学概念之间的关系。本文通过对全球 100 年来在 G. N. 刘易斯关于《原子与分子》的开创性论文（Lewis，G. N.，The Atom and the Molecule，J. Am. Chem. Soc.，1916，38，762-785）的研究，探讨了这一目标所产生的详细化学见解，重点介绍了如何通过应用键合演变理论（BET）来确定反应机制，强调了在化学反应机制中如何用弯箭头表示电子密度转移，以及如何恢复路易斯结构。BET 结合电子定域函数（ELF）的拓扑分析和 Thom 突变理论（CT），为深入了解化学重排的分子机制提供了强大的工具。BET 符合物理定律和量子理论的见解，可以被认为是解决具有广泛应用可能性的化学反应性的合适工具。同样，本方法还恢复了用于给定反应机制的描述化学键重排的经典弯箭头，为这种表示形式提供了详细的物理基础。应用于非平衡几何形状的价层电子对排斥（VSEPR）模型所基于的思想为密度转移提供了简单的化学解释。对于中心原子周围的给定几何形状，电子域的排列可能符合或不符合所考虑原子的价壳层电子数的 VSEPR 规则。变形会产生 VSEPR 有缺陷的排列（至少缺少一个域来匹配与配体几何形状对应的 VSEPR 排列）、VSEPR 符合或伪 VSEPR，此时键合和非键合域的位置相互交换。VSEPR 有缺陷的排列增加了位点的亲电性，而 VSEPR 符合的排列则预示着新共价键的形成。解释反应坐标的正则模态的频率提供了关于密度转移顺序的附加信息。该简单模型产生的结果与 BET 得到的结果非常吻合。
