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三氟苯乙烯(TFS)的热环化二聚反应是经过1,4-双自由基机理进行的。这一反应的溶剂效应和取代基效应已对此提供了有力的证据。此反应体系又具有一些与众不同的特色,如:(1)取代 TFS 的~(19)F NMR 参数可以直接反映双键π电子云的极化程度;(2)热环化二聚反应的过渡态具有偶极上的对称
The thermal cycloaddition reaction of trifluorostyrene (TFS) proceeds via the 1,4-diradical mechanism. The solvent effects and substituent effects of this reaction have provided strong evidence for this. The reaction system also has some distinctive features, such as: (1) The ~ (19) F NMR parameters of the TFS can directly reflect the degree of polarization of the double bond π electron cloud; (2) Transition states have dipole symmetry