We describe a unified picture of symmetry-breaking electronic interactions that are usually described as “pseudo-Jahn–Teller (PJT) effects” and attributed to vibronic coupling but can also be associated with hyperconjugative donor–acceptor interactions in the framework of natural bond orbital (NBO) and natural resonance theory (NRT) analysis. We show how NBO/NRT descriptors offer a simplified alternative to the vibronic coupling picture of PJT effects that yields both improved cause–effect specificity and chemically enriched understanding of symmetry-breaking phenomena but with no necessary input from ground-state vibrational or excited-state electronic properties. Comparative NBO/NRT vs vibronic coupling analyses of PJT effects are illustrated for two well-known cases: trans-bending in Si₂H₄ and higher Group-14 homologues of ethylene and chain-kinking in cyclopentadienylideneketene (C₅H₄CCO) and related cumulene ketones. The conceptual and practical advantages of the NBO-based hyperconjugative approach may be expected to extend to numerous PJT-type symmetry-breaking phenomena throughout the chemical sciences.

中文翻译：

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伪Jahn–Teller效应的自然键轨道理论

我们描述了对称性破坏的电子相互作用的统一图景，通常被描述为“伪Jahn–Teller（PJT）效应”，归因于振动耦合，但也可能与自然键轨道框架中的超共轭施主-受体相互作用相关。 （NBO）和自然共振理论（NRT）分析。我们将展示NBO / NRT描述符如何提供PJT效应的电子耦合图的简化替代方案，该方案既可以改善因果关系特异性，又可以通过化学方式丰富理解对称性破坏现象，但无需从基态振动或激发态获得必要的输入电子特性。比较了两种众所周知的情况的PJT效应的NBO / NRT与振动耦合比较分析：Si ₂ H _4中的反式弯曲以及在环戊二烯基亚烯基烯（C ₅ H ₄ CCO）和相关的枯烯酮中乙烯和链结的更高的第14组同系物。基于NBO的超共轭方法的概念和实践优势可望扩展到整个化学科学中的许多PJT型对称性破坏现象。