Annulenes and their charged analogs play an important role in validating Hückel's aromaticity rule. Whereas annulenes with [4n + 2] π electrons tend to delocalize π electron density, annulenes with [4n] π electrons prefer to form local double bonds (bond alternation) resulting in two interconvertible valence isomers. However, it is very challenging to experimentally detect such a valence tautomerization process as a result of the very fast conversion. In this work, we synthesized a series of [n]cyclo-para-biphenylmethine macrocycles ([n]CPBM-An, n = 3–8) as analogs of [n]annulenes and observed the unusual valence tautomerization process by variable-temperature NMR measurements for [4]CPBM-An, which showed a moderate interconversion barrier (11.22 kcal/mol at coalescence temperature) via a C₄ tetraradicaloid transition state. These macrocycles showed [n]annulene-like geometries but with unique open-shell polyradical character. Their optical, electrochemical, and magnetic properties were systematically investigated and compared with those of the recently studied [n]cyclo-para-phenylenes.

Annulenes及其带电荷的类似物在验证Hückel的芳香性规则中起着重要作用。具有[4 n  + 2]π电子的环烯倾向于使π电子密度离域，而具有[4 n ]π电子的环烯更倾向于形成局部双键（键交替），从而导致两个可相互转换的化合价异构体。然而，由于非常快速的转化，通过实验检测这样的价互变异构过程是非常具有挑战性的。在这项工作中，我们合成了一系列[n]环-对-联苯甲氨酸大环（[n] CPBM-An，n = 3-8）作为[n]环戊烯的类似物，并观察到了可变温度下不寻常的价互变异构过程[4] CPBM-An的NMR测量，通过C ₄四氢基态过渡态显示出适度的互转换垒（在聚结温度下为11.22 kcal / mol）。这些大环化合物显示[n]环戊烯状的几何形状，但具有独特的开壳多自由基特征。对它们的光学，电化学和磁性进行了系统的研究，并与最近研究的[n]环-对-亚苯基的化合物进行了比较。