Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Department of Pharmacy, Health Services Vocational School, Sivas Cumhuriyet University, 58140 Sivas, Turkey.
J Phys Chem A. 2020 Dec 24;124(51):10897-10908. doi: 10.1021/acs.jpca.0c08196. Epub 2020 Dec 10.
We investigate the physical basis, validity, and limitations of the minimum electrophilicity principle, MEP, which postulates that the sum of the electrophilicity indices, ∑ω, of the reaction products will be smaller than that of the reactants, Δω < 0. We present a much-improved understanding of the conditions for minimizing electrophilicity indices. Two indices, ω = ( + )/8( - ) and ω = ·/( - ), are discussed, using ionization energies, , and electron affinities, , obtained from either ground-state (GS) or valence-state (VS) energies. The performances of ω and ω are compared for a wide range of chemical species from diatomic molecules, through large clusters to liquid water and solid crystals. New analytical arguments in support of MEP are found. Two new theorems are proved, and three new rules rationalize the changes Δω and Δω in association reactions, X + Y → XY. They explain why MEP is much more successful as a guiding rule than the maximum hardness postulate in such reactions. On the other hand, they also identify the increased electron affinity of the product as the reason for the rare but highly significant failures of MEP, e.g., in B, C, Si, and CN. As a rule, electrophilicity is minimized in association reactions. However, both ω and ω are increased if the bond dissociation energy (XY) is larger than (XY), which is equivalent to an increased product electron affinity. The large positive changes Δω and Δω in 2C → C exhibit a strong contrast to MEP. The changes in electrophilicity indices may help gain insights into the versatility of the chemistries of carbon and other elements. Solid-state double-exchange reactions are correctly assessed by Kaya's composite descriptor, somewhat less by ω, but not at all by ω. A wide class of failures of MEP is found as size-driven electrophilicity maximization, Δω > 0, e.g., in fullerenes, large metal clusters, and liquid water. Many electrophiles, especially superelectrophiles, show significantly larger electrophilicity indices than the largest index of their isolated atoms. The changes Δω and Δω provide important information on the reactivities of chemical systems; however, it appears that the minimum electrophilicity postulate cannot serve as a basis for a theory.
我们研究了最小电负性原理（MEP）的物理基础、有效性和局限性，该原理假定反应产物的电负性指数之和（∑ω）将小于反应物的电负性指数之和（Δω<0）。我们对最小化电负性指数的条件有了更深入的理解。讨论了两个指数ω=（+）/8（-）和ω=·/（-），使用从基态（GS）或价态（VS）能量中获得的电离能（）和电子亲合能（）。比较了ω和ω在从双原子分子到大分子团簇、液态水和固态晶体等广泛化学物质中的性能。找到了支持 MEP 的新的分析论点。证明了两个新定理，并提出了三个新规则来合理化加成反应 X+Y→XY 中Δω和Δω的变化。它们解释了为什么 MEP 作为指导规则在这些反应中比最大硬度假设更为成功。另一方面，它们还确定了产物的增加电子亲合性是 MEP 罕见但高度显著失效的原因，例如在 B、C、Si 和 CN 中。通常情况下，在加成反应中电负性最小化。然而，如果键解离能（XY）大于（XY），则ω和ω都会增加，这相当于增加了产物的电子亲合性。2C→C 中较大的正变化Δω和Δω与 MEP 形成强烈对比。电负性指数的变化可以帮助深入了解碳和其他元素化学的多功能性。Kaya 的综合描述符可以正确评估固态双交换反应，ω 的评估稍差，但 ω 则完全无法评估。发现了 MEP 的广泛失效类别，例如尺寸驱动的电负性最大化，Δω>0，例如在富勒烯、大金属团簇和液态水中。许多亲电试剂，特别是超强亲电试剂，表现出比其孤立原子的最大指数更大的电负性指数。变化Δω和Δω提供了有关化学系统反应性的重要信息；然而，似乎最小电负性假设不能作为理论的基础。
