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结构流变是化学中熟知的现象,但人们对分子流变过程的成键本质尚认识不足.文章提出化学中的“流变键”(Fluxional Bonds,FBs)概念,并将其成功应用于平面、笼状和管状硼团簇及瞬烯分子C10H10,揭示了化学结构流变的成键本质.与传统的由于化学键的伸缩、弯曲和摇摆等产生的Berry准旋转不同,流变键在一定条件下可以不断地破裂和生成,是分子结构流变的驱动力.文章继续研究瞬烯类似物C9H9+、C9BH9和C8NH9中的流变键,在分子轨道水平上揭示其流变机理.详尽的轨道和成键分析表明,这些模型化合物中存在与瞬烯相似的流变键.在从基态(GS)到过渡态(TS)的流变过程中,C9H9+主要涉及两个流变σ键的变化(GS(1 2c-2eσ+1 3c-2e σ)→TS(2 2c-2eσ)→GS'(1 2c-2e σ+1 3c-2e σ)),而C9BH9和C8NH9则是两个π键(GS(2 2c-2eπ)→TS(2 3c-2e π)→GS'(2 2c-2eπ))和一个σ键(GS(1 2c-2e σ)→TS(1 4c-2e σ)→GS'(1 2c-2e σ))协同流变的结果.流变键采用联系、运动和变化的观点分析化学成键,是对化学中传统定域和离域成键概念的拓展,预计在催化、纳米材料和分子马达研究中具有重要意义.“,”Chemical bond is the most important concept in chemistry.This paper proposed the concept offluxional bonds which form and break constantly under certain conditions and applied it successfully to various boron clusters and bullvalene C10H10,unveiling the fluxional bonding nature of these important species.We continue in this work to explore the fluxional bonds in analogs ofbullvalene,C9H9+,C9BH9 and C8NH9,to reveal the bonding fluctuation mechanisms of these interesting species at molecular orbital level.The detailed brbital and bonding analyses indicate that the fluxional bonds of these model compounds exhibit obvious similarity with that of bullvalene.The fluxional process of C9H9+ mainly involves two fluxional σ-bonds from the ground state (GS) to transition state (TS) (GS(1 2c-2e σ + 1 3c-2e σ) → TS(2 2c-2e σ) → GS'(1 2c-2e σ + 1 3c-2e σ)),while the fluctuations of both C9BH9 and C8NH9 involve two fluxional π-bonds (GS(2 2c-2e π) → TS(2 3c-2e π) →GS'(2 2c-2e π)) and one fluxional σ-bond (GS(1 2c-2e σ) → TS(1 4c-2e σ) → GS'(1 2c-2e σ)) in concerted mechanisms.