Kinetic parameters for sulfur inversion in the title compound were determined by the dynamic NMR method in CD2CL2 as follows: ΔH≠ 14.2±0.1 kcal mol−1, ΔS≠ 11.3±0.3 cal mol−1 K−1, ΔG233≠ 11.6 kcal mol−1. The large and positive entropy of activation suggests that the inversion takes place through dissociative mechanisms. Comparison of the rate constants obtained with multiple probes shows that the rotation about the Cph–B bond requires further energy after the dissociation of the S–B bond. The solvent effect on the sulfur inversion is small but distinct; the more polar a solvent, the higher the barrier to the inversion. Dynamic behaviors of a related compound are also discussed.
标题化合物中
硫反转的动力学参数是在 CD2C
L2 中通过动态核磁共振法测定的,具体如下ΔH≠14.2±0.1 kcal mol-1,ΔS≠11.3±0.3 cal mol-1 K-1,ΔG233≠11.6 kcal mol-1。较大的正活化熵表明,反转是通过解离机制进行的。比较多个探针得到的速率常数表明,在 S-B 键解离后,围绕 Cph-B 键的旋转需要更多的能量。溶剂对
硫反转的影响很小,但很明显;溶剂的极性越大,反转的障碍就越高。此外还讨论了一种相关化合物的动态行为。