Aromaticity of tropylium derivatives: When and why might captodative structures be preferred over the isomeric push-pull structures?

IF 2.3 3区 化学 Q3 CHEMISTRY, PHYSICAL International Journal of Quantum Chemistry Pub Date : 2024-07-25 DOI:10.1002/qua.27449
Bagrat A. Shainyan
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Abstract

An intriguing question in the general problem of aromaticity is whether captodative aromatic systems with the donor and acceptor substituents at the same carbon of the CC bond can be more stable than the π-conjugated push-pull counterparts? The analysis of electronic, magnetic, and structural criteria of aromaticity showed that for conventional organic substituents XO, TfN, (NC)2C, (NO2)2C, Tf2C, the push-pull tropylidene derivatives [tropylium]+CHCHX are expectedly more stable than their captodative isomers [tropylium]+C(X)CH2, with the lowest ΔE for the most strong acceptor Tf2C. A different behavior is observed for XMHlg3 (MB, Al; HlgF, Cl). They are not only structurally and magnetically most aromatic in both series but show the inverse stability of the push-pull and captodative isomers, the latter being more stable by up to 10 kcal/mol (in gas).The difference between the MHlg3 groups and conventional organic groups is that in the latter the electron density is transferred to the π-system of the substituent, while the former can accept it only to the σ*(CM) orbital. Thus, when the electron donor and acceptor effects are separated between the σ and π systems, captodative isomers can be more stable than their push-pull isomers with more extended conjugation.

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托品鎓衍生物的芳香性:什么时候以及为什么俘获结构比异构推拉结构更受青睐?
在芳香性的一般问题中,一个耐人寻味的问题是,供体和受体取代基位于 CC 键的同一碳上的俘获芳香系统是否会比π共轭推挽式芳香系统更稳定?对芳香性的电子、磁性和结构标准的分析表明,对于传统的有机取代基 XO、TfN、(NC)2C、(NO2)2C、Tf2C,推挽亚托品衍生物 [托品]+CHCHX-预期比它们的俘获异构体 [托品]+C(X-)CH2 更稳定,对于最强的受体 Tf2C,ΔE 最低。XMHlg3(MB,Al;HlgF,Cl)的行为则有所不同。MHlg3 基团与传统有机基团的区别在于,后者的电子密度转移到取代基的 π 系统,而前者只能接受电子密度转移到 σ*(CM) 轨道。因此,当电子供体和受体效应在 σ 和 π 系统之间分离时,俘获异构体可能比具有更多扩展共轭的推拉异构体更稳定。
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来源期刊
International Journal of Quantum Chemistry
International Journal of Quantum Chemistry 化学-数学跨学科应用
CiteScore
4.70
自引率
4.50%
发文量
185
审稿时长
2 months
期刊介绍: Since its first formulation quantum chemistry has provided the conceptual and terminological framework necessary to understand atoms, molecules and the condensed matter. Over the past decades synergistic advances in the methodological developments, software and hardware have transformed quantum chemistry in a truly interdisciplinary science that has expanded beyond its traditional core of molecular sciences to fields as diverse as chemistry and catalysis, biophysics, nanotechnology and material science.
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