Zalazar M Fernanda, Peruchena Nélida M
Laboratorio de Estructura Molecular y Propiedades, Area de Química Física, Departamento de Química, Facultad de Ciencias Exactas, Naturales y Agrimensura, Universidad Nacional del Nordeste, Avda Libertad 5460, (3400) Corrientes, Argentina.
J Phys Chem A. 2007 Aug 16;111(32):7848-59. doi: 10.1021/jp071659v. Epub 2007 Jul 20.
In the present work, the distribution of the electronic charge density in the ethene protonation reaction by a zeolite acid site is studied within the framework of the density functional theory and the atoms in molecules (AIM) theory. The key electronic effects such as topological distribution of the charge density involved in the reaction are presented and discussed. The results are obtained at B3LYP/6-31G(**) level theory. Attention is focused on topological parameters such as electron density, its Laplacian, kinetic energy density, potential energy density, and electronic energy density at the bond critical points (BCP) in all bonds involved in the interaction zone, in the reactants, pi-complex, transition state, and alkoxy product. In addition, the topological atomic properties are determined on the selected atoms in the course of the reaction (average electron population, N(Omega), atomic net charge, q(Omega), atomic energy, E(Omega), atomic volume, v(Omega), and first moment of the atomic charge distribution, M(Omega)) and their changes are analyzed exhaustively. The topological study clearly shows that the ethene interaction with the acid site of the zeolite cluster, T5-OH, in the ethene adsorbed, is dominated by a strong O-H...pi interaction with some degree of covalence. AIM analysis based on DFT calculation for the transition state (TS) shows that the hydrogen atom from the acid site in the zeolitic fragment is connected to the carbon atom by a covalent bond with some contribution of electrostatic interaction and to the oxygen atom by closed shell interaction with some contribution of covalent character. The C-O bond formed in the alkoxy product can be defined as a weaker shared interaction. Our results show that in the transition state, the dominant interactions are partially electrostatic and partially covalent in nature, in which the covalent contribution increases as the concentration and accumulation of the charge density along the bond path between the nuclei linked increases.
在本工作中，在密度泛函理论和分子中的原子（AIM）理论框架内，研究了乙烯在沸石酸位点质子化反应中电子电荷密度的分布。给出并讨论了反应中涉及的电荷密度拓扑分布等关键电子效应。结果是在B3LYP/6 - 31G（**）理论水平下获得的。重点关注相互作用区域、反应物、π络合物、过渡态和烷氧基产物中所有键的键临界点（BCP）处的拓扑参数，如电子密度、其拉普拉斯算子、动能密度、势能密度和电子能量密度。此外，确定了反应过程中所选原子的拓扑原子性质（平均电子布居数，N(Ω)，原子净电荷，q(Ω)，原子能量，E(Ω)，原子体积，v(Ω)，以及原子电荷分布的一阶矩，M(Ω)），并详尽分析了它们的变化。拓扑研究清楚地表明，在乙烯吸附状态下，乙烯与沸石簇的酸位点T5 - OH的相互作用主要由具有一定共价性的强O - H...π相互作用主导。基于密度泛函理论计算对过渡态（TS）的AIM分析表明，沸石片段中酸位点的氢原子通过具有一定静电相互作用贡献的共价键与碳原子相连，并通过具有一定共价特征贡献的闭壳层相互作用与氧原子相连。在烷氧基产物中形成的C - O键可定义为较弱的共享相互作用。我们的结果表明，在过渡态中，主要相互作用本质上部分是静电的，部分是共价的，其中共价贡献随着沿相连原子核之间键路径的电荷密度的浓度和积累增加而增加。
