Li Chen, Xin Xin, Wang Dunyou
College of Physics and Electronics, Shandong Normal University, Jinan, Shandong 250014, China.
Phys Chem Chem Phys. 2021 Oct 20;23(40):23267-23273. doi: 10.1039/d1cp03048e.
We investigated the S2 Walden-inversion mechanism of X (X = SH, PH) + CHY (Y = F, Cl, Br, I) reactions in water using multi-level quantum mechanics (ML-QM) and molecular mechanics (MM) methods. The potentials of the mean force were mapped using not only the density functional theory (DFT)/MM method but also a high-level, accurate CCSD(T)/MM method using the aug-cc-pVTZ basis set. In particular, for the PH + CHI reaction, although the backside attack Walden-inversion mechanics were not observed in the gas phase, we found that this mechanism takes place in water. The atomic-level dynamics of the concerted S2 mechanism and the stationary points along the reaction paths were characterized. For these reactions in water, their Walden-inversion barriers are higher than their corresponding ones in the gas phase, indicating that the aqueous solution hinders their reactivity. For the reactions with the same nucleophile X in water, the reaction barrier heights with different leaving groups are in the order of F > Cl > Br > I. For the same leaving group Y with different nucleophiles SH and PH, the reaction barrier with SH is greater than that of PH due to the former having higher electronegativity than the latter.
我们使用多级量子力学（ML-QM）和分子力学（MM）方法，研究了水中X（X = SH，PH）+ CHY（Y = F，Cl，Br，I）反应的S2瓦尔登反转机制。不仅使用密度泛函理论（DFT）/MM方法，还使用使用aug-cc-pVTZ基组的高水平精确CCSD（T）/MM方法绘制平均力势。特别是对于PH + CHI反应，尽管在气相中未观察到背面进攻的瓦尔登反转机制，但我们发现该机制在水中发生。表征了协同S2机制的原子水平动力学以及沿反应路径的驻点。对于这些在水中的反应，它们的瓦尔登反转势垒高于气相中的相应势垒，表明水溶液阻碍了它们的反应性。对于水中具有相同亲核试剂X的反应，具有不同离去基团的反应势垒高度顺序为F > Cl > Br > I。对于具有不同亲核试剂SH和PH的相同离去基团Y，由于SH的电负性高于PH，SH的反应势垒大于PH的反应势垒。
