The dynamics of the allylic rearrangement of the (1,3-diphenylallyl)dimethylsulfonium ion in CD₂Cl₂, which proceeds via intermediate 1,3-diphenylallyl cations, has been investigated by variable temperature ¹H NMR spectroscopy. At low temperature, the three allylic protons give rise to an AMX system, and the two diastereotopic S-methyl groups resonate at different frequencies. At higher temperature, an AX₂ system for the allylic protons and a single signal for the S-methyl groups are observed. The resulting exchange rate constant of (364 ± 2) s^–1 at 25°C, which corresponds to the rate of the heterolytic cleavage of the C–S bond, was used to explore the range of validity of the linear free energy relationship log k_het(25°C) = s_f (N_f + E_f), which describes the rates of heterolytic cleavages by the electrofugality parameter E_f and the solvent-dependent nucleofuge-specific parameters N_f and s_f. The observed rate constant corroborates a previous conclusion that two different sets of N_f and s_f parameters may exist for the same nucleofuge. Knowledge of whether the reverse bond-forming reaction occurs under activation or under diffusion control is crucial for the choice of the appropriate set of nucleofugality parameters.

中文翻译：

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(1,3-二苯基烯丙基)二甲基锍离子的二甲基硫醚交换动力学

通过变温¹ H NMR 光谱研究了 CD ₂ Cl ₂中 (1,3-二苯基烯丙基) 二甲基锍离子的烯丙基重排动力学，该重排通过中间体 1,3-二苯基烯丙基阳离子进行。在低温下，三个烯丙基质子产生 AMX 系统，两个非对映体S-甲基基团以不同的频率共振。在较高温度下，观察到烯丙基质子的 AX _2系统和S-甲基基团的单一信号。所得汇率常数为 (364 ± 2) s ^–1在 25°C，对应于 C-S 键的异裂速率，用于探索线性自由能关系 log k _het (25°C) =  s _f ( N _f  +  E _{f ），它描述了由电离参数}E _f和溶剂相关的离核剂特定参数N _f和s _f引起的异裂速率。观察到的速率常数证实了先前的结论，即两组不同的N _f和s _f相同的nucleofuge 可能存在参数。了解反向成键反应是在活化下还是在扩散控制下发生对于选择适当的核逸散性参数集至关重要。