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建立自由基反应中取代基的自旋离域参数σ°,是自由基化学中的根本问题之一。多年来,许多人试图通过动力学或谐学的方法来解决这一问题,但至今还没有一个令人满意的体系能拆分取代基的极性效应和自旋离域效应。蒋锡夔、计国桢等通过对取代三氟苯乙烯的~(19)F NMR参数的分析和热环化二聚反应的动力学研究,提出了一条可能较为合理的建立O°的新途径。他们和前人的工作都采用了通用的假设——问位取代基没有自旋
Establishing the spin delocalization parameter σ ° of the substituent in the radical reaction is one of the fundamental problems in free radical chemistry. Over the years, many people have tried to solve this problem through kinetic or harmonic methods, but so far no satisfactory system has been available to separate the polar effects of polar substituents and spin-delocalization effects. Jiang Xun, Ji Guozhen et al. By analyzing the ~ (19) F NMR spectra of the substituted trifluorostyrene and the kinetics of the thermal cycloaddition reaction, a new approach to establish O ° may be proposed. They and their predecessors all took the common assumption that spin substitutions did not spin