Laboratoire de RMN Haute Résolution CP 160/08, Université Libre de Bruxelles, Av. F.-D. Roosevelt 50, 1050 Brussels, Belgium.
Molecules. 2012 Oct 26;17(11):12718-33. doi: 10.3390/molecules171112718.
Bis(acetoxy)iodobenzene and related acyloxy derivatives of hypervalent I(III) were studied by variable temperature solution-state ¹⁷O-NMR and DFT calculations. The ¹⁷O-NMR spectra reveal a dynamic process that interchanges the oxygen atoms of the acyloxy groups. For the first time, coalescence events could be detected for such compounds, allowing the determination of activation free energy data which are found to range between 44 and 47 kJ/mol. The analysis of the ¹⁷O linewidth measured for bis(acetoxy)iodobenzene indicates that the activation entropy is negligible. DFT calculations show that the oxygen atom exchange arises as a consequence of the [1,3]-sigmatropic shift of iodine. The calculated activation barriers are in excellent agreement with the experimental results. Both the ¹⁷O-NMR and DFT studies show that the solvent and chemical alterations, such as modification of the acyl groups or para- substitution of the benzene ring, hardly affect the energetics of the dynamic process. The low I-O Wiberg bond index (0.41-0.42) indicates a possible explanation of the invariance of both the energy barrier and the ¹⁷O chemical shift with para-substitution.
双（乙酰氧基）碘苯和高价碘（III）的相关酰氧基衍生物通过变温溶液状态¹⁷O-NMR 和 DFT 计算进行了研究。¹⁷O-NMR 光谱揭示了一个动态过程，其中酰氧基基团的氧原子发生交换。首次可以检测到此类化合物的合并事件，从而可以确定活化自由能数据，这些数据发现范围在 44 到 47 kJ/mol 之间。对双（乙酰氧基）碘苯测量的¹⁷O 线宽的分析表明，活化熵可以忽略不计。DFT 计算表明，氧原子交换是由于碘的[1,3]-σ迁移引起的。计算出的活化势垒与实验结果非常吻合。¹⁷O-NMR 和 DFT 研究均表明，溶剂和化学变化，例如酰基的修饰或苯环的对位取代，几乎不会影响动态过程的能量学。低的 I-O Wiberg 键指数（0.41-0.42）表明，对位取代对能垒和¹⁷O 化学位移的不变性可能有一个解释。
