Johnson Lucius E, DuPré Donald B
Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
J Phys Chem A. 2008 Aug 14;112(32):7448-54. doi: 10.1021/jp802214u. Epub 2008 Jul 18.
Previous analysis of the topology of the electron density of bis(dimethylamino)cyclopropenylidene as a model of the stable bis(diisopropylamino)cyclopropenylidene revealed mechanisms of induction/back-polarization, sigma-aromaticity, and sigma-pi polarization to be responsible for the electronic stabilization of the divalent carbon C2 upon amino substitution on the 3MR. This work presents new data from molecular orbital calculations and a full analysis of the operative natural bond orbitals and their interactions. The discrepancies between these orbital-based stabilization mechanisms and the physical stabilization based upon the quantum theory of atoms in molecules are uncovered through the separation of electron localization and delocalization indices into contributions from orbitals of sigma- and pi-symmetry, as well as calculated nucleus-independent chemical shifts that determine the degree of sigma- and pi-delocalization/aromaticity. Graphical representations of functions of the electron density mapped onto various pi-orbital isosurfaces serve to better visualize the underlying differences between mathematical orbital space and the real space of the electron density. This work also provides new insight into the topological-based mechanism through investigation of the changes in the virial of the electronic forces acting on the interatomic surfaces--forces that govern the bonding and stabilization within a molecule.
先前对双（二甲基氨基）环丙烯叉作为稳定的双（二异丙基氨基）环丙烯叉模型的电子密度拓扑结构的分析揭示了诱导/反向极化、σ-芳香性和σ-π极化机制，这些机制导致了在3MR上进行氨基取代时二价碳C2的电子稳定化。这项工作展示了分子轨道计算的新数据以及对有效自然键轨道及其相互作用的全面分析。通过将电子定域化和离域化指数分离为σ-和π-对称轨道的贡献，以及计算确定σ-和π-离域化/芳香性程度的核独立化学位移，揭示了这些基于轨道的稳定化机制与基于分子中原子量子理论的物理稳定化之间的差异。将电子密度函数映射到各种π-轨道等值面上的图形表示有助于更好地可视化数学轨道空间与电子密度实际空间之间的潜在差异。这项工作还通过研究作用于原子间表面的电子力的维里变化，为基于拓扑的机制提供了新的见解，这些力控制着分子内的键合和稳定化。
