Bühl Michael, Wipff Georges
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany.
J Am Chem Soc. 2002 Apr 24;124(16):4473-80. doi: 10.1021/ja012428j.
A quantum-chemical study employing the BLYP density functional is reported for the complex of H3O+ with 18-crown-6. According to a Car-Parrinello molecular dynamics (CPMD) study at 340 K, the complex is quite flexible, and is characterized by three quasi-linear (two-center) hydrogen-bond interactions for most of the time. On a time scale of 10 ps, frequent inversions of H3O+ are observed, as well as two 120 degrees rotations switching the hydrogen bonds from one set of crown-ether O atoms to the other. These results are consistent with density-functional studies of stationary points on the potential energy surface, which show how the crown "catalyzes" the guest's inversion. Two close-lying minima are characterized, as well as two distinct transition states connecting them, either via H3O+ inversion or rotation, with barriers of 1.0 and 4.6 kcal/mol, respectively, at the BLYP/II'//BLYP/6-31G level. Orbital interactions between lone pairs on ether O atoms and hydronium sigma(OH) antibonding orbitals are important factors for the directionality of the hydrogen bonds.
本文报道了一项采用BLYP密度泛函的量子化学研究，研究对象是H3O+与18-冠-6的配合物。根据在340 K下进行的Car-Parrinello分子动力学（CPMD）研究，该配合物具有相当高的灵活性，并且在大部分时间内以三种准线性（双中心）氢键相互作用为特征。在10 ps的时间尺度上，观察到H3O+频繁反转，以及两次120度旋转，使氢键从一组冠醚O原子切换到另一组。这些结果与势能面上驻点的密度泛函研究一致，该研究表明冠醚如何“催化”客体的反转。表征了两个紧邻的极小值，以及通过H3O+反转或旋转连接它们的两个不同的过渡态，在BLYP/II'//BLYP/6-31G水平下，势垒分别为1.0和4.6 kcal/mol。醚O原子上的孤对电子与水合氢离子σ(OH)反键轨道之间的轨道相互作用是氢键方向性的重要因素。
