Hyperconjugation, a weak interaction in organic chemistry, can have a strong effect on aromaticity, leading to the concept of hyperconjugative aromaticity, which was first proposed by Mulliken in 1939. However, most studies are limited to main group chemistry. Here we report the most aromatic and antiaromatic pyrrolium ring by maximizing the hyperconjugation caused by transition metal fragments and the push–pull effect. Our calculations reveal that the origin of the outperformance of transition metal substituents over main group ones on hyperconjugative aromaticity could be attributed to their higher highest occupied molecular orbitals (HOMOs). Among the group 11 transition metals, a silver substituent results in the best performance. All these findings highlight the magic of the transition metal (silver) and could be particularly helpful for the design of other aromatic and antiaromatic counterparts based on a nonaromatic parent species.

中文翻译：

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通过最大程度地发挥超共轭和推挽效应来探索最芳香和最芳香的吡咯环

超共轭是有机化学中较弱的相互作用，可能对芳香性有很强的影响，从而导致了超共轭芳香性的概念，这是Mulliken在1939年首次提出的。但是，大多数研究仅限于主化学。在这里，我们通过最大化过渡金属碎片和推挽效应引起的超共轭作用，报告了最芳族和最芳族的吡咯环。我们的计算表明，过渡金属取代基在超共轭芳香性上优于主要基团的原因可能归因于其较高的最高占据分子轨道（HOMO）。在第11族过渡金属中，银取代基导致最佳性能。