National Medicines Institute, 30/34 Chełmska Street, 00-725 Warsaw, Poland.
Org Biomol Chem. 2013 May 14;11(18):2997-3013. doi: 10.1039/c3ob00017f.
New descriptors of the double bonded substituent effect, sEDA(=) and pEDA(=), were constructed based on quantum chemical calculations and NBO methodology. They show to what extent the σ and π electrons are donated to or withdrawn from the substituted system by a double bonded substituent. The new descriptors differ from descriptors of the classical substituent effect for which the pz orbital of the ipso carbon atom is engaged in the π-electron system of the two neighboring atoms in the ring. For double bonded substituents, the pz orbital participates in double bond formation with only one external atom. Moreover, the external double bond forces localization of the double bond system of the ring, significantly changing the core molecule. We demonstrated good agreement between our descriptors and the Weinhold and Landis' "natural σ and π-electronegativities": so far only descriptors allowing for evaluation of the substitution effect by a double bonded atom. The equivalency between descriptors constructed for 5- and 6-membered model structures as well as linear dependence/independence of the constructed parameters was discussed. Some interrelations between sEDA(=) and pEDA(=) and the other descriptors of (hetero)cyclic systems such as aromaticity and electron density in the ring and bond critical points were also examined.
基于量子化学计算和 NBO 方法，构建了新的双键取代基效应描述符 sEDA(=) 和 pEDA(=)。它们表示双键取代基向取代体系贡献或从取代体系提取 σ 和 π 电子的程度。这些新描述符与经典取代基效应的描述符不同，经典取代基效应的描述符涉及到取代体系中 ipso 碳原子的 pz 轨道参与到环中两个相邻原子的π电子系统中。对于双键取代基，pz 轨道仅与一个外部原子形成双键。此外，外部双键迫使环的双键系统局部化，显著改变了核心分子。我们证明了我们的描述符与 Weinhold 和 Landis 的“自然 σ 和 π 电负性”之间的良好一致性：迄今为止，只有允许通过双键原子评估取代基效应的描述符。讨论了为 5 元和 6 元模型结构构建的描述符之间的等效性，以及构建参数的线性依赖性/独立性。还检查了 sEDA(=)和 pEDA(=)与（杂）环系统的其他描述符（如芳香性和环中的电子密度以及键临界点）之间的一些关系。
