Electronic perturbations of the aromatic nucleus: Hammett constants and electrostatic potential topography
Electronic perturbations of the aromatic nucleus: Hammett constants and electrostatic potential topography
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DOI：
10.1021/jo961679l
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发表时间：
1997-04-18
影响因子：
3.6
通讯作者：
Suresh, CH
中科院分区：
文献类型：
--
作者：
Gadre, SR;Suresh, CH
连接到苯核上的取代基能够扰乱该核内的电子分布。取代基常数首先由Hammett引入，[1]给出了这些电子扰动的度量。最广泛使用的取代基常数是σ m和σ p，它们分别从间位和对位取代的苯甲酸的解离常数数据获得。Hammett参数在研究和解释数千种有机反应和机制2中的成功，强调了取代基在不同化学体系中扰乱苯核电子环境的一致性。一位有机化学家用电感效应和共振效应经典地解释了这些微扰。这些电子扰动通过将它们与计算的量如总能量、原子电荷、静电势等相关联而得到了很好的研究，从从头算量子化学或半经验方法得到。3最近，Haeberlein和Brinck分析了对位取代酚盐离子中的取代基效应，发现在酚盐氧附近观察到的静电势最小值Vmin与气相酸度之间存在密切的线性关系。然而，他们没有考虑取代基引起的芳环上的电子扰动。在本工作中，我们提出了一种基于单取代苯分子静电势（MESP）拓扑结构直接评估取代基对芳香族π电子分布的影响的方法，MESP是一种用于探索分子反应性，分子间相互作用和各种其他化学现象的成熟工具。[5] Politzer等人广泛使用它来理解一般的亲电取代反应，特别是取代苯和许多其他化学应用。6-10平均局部电离能也用于此目的。最近，Gadre等人提出，
A substituent attached to a benzene nucleus is capable of perturbing the electronic distribution within that nucleus. Substituent constants, first introduced by Hammett, 1 give a measure of these electronic perturbations. The most widely used substituent constants are σm and σp which are obtained from the dissociation constant data of the meta-and para-substituted benzoic acids, respectively. The success of the Hammett parameters for the study and interpretation of thousands of organic reactions and mechanisms2 underlines the consistency of a substituent to perturb the electronic environment of the benzene nucleus in different chemical systems. An organic chemist explains these perturbations classically in terms of inductive and resonance effects. These electronic perturbations were well-studied by correlating them with computed quantities such as total energy, atomic charges, electrostatic potentials, etc., derived from either ab-initio quantum chemical or semiempirical methods. 3 Very recently, Haeberlein and Brinck4 have analyzed the substituent effects in para-substituted phenoxide ions and found a close, linear relation between the minima of the electrostatic potential, Vmin, observed near the phenoxide oxygen and the gas phase acidities. However, they have not considered the electronic perturbations occurring over the aromatic ring due to a substituent. In the present work, we propose a method for directly assessing the effect of a substituent on the aromatic π-electron distribution based on the molecular electrostatic potential (MESP) topography of monosubstituted benzenes.MESP is a well-established tool for exploring molecular reactivities, intermolecular interactions, and a variety of other chemical phenomena. 5 It has been extensively used by Politzer et al. for understanding the general electrophilic substitution reactions, in particular for substituted benzenes and many other chemical applications. 6-10 Average local ionization energy has also been employed11 for this purpose. Recently, Gadre et al. have proposed