Udagawa Taro, Ishimoto Takayoshi, Tokiwa Hiroaki, Tachikawa Masanori, Nagashima Umpei
Quantum Chemistry Division, Graduate School of Science, Yokohama-City University, Kanazawa-ku, Kanagawa, Japan.
J Phys Chem A. 2006 Jun 8;110(22):7279-85. doi: 10.1021/jp0615656.
The geometric isotope effect (GIE) of sp- (acetylene-water), sp(2)- (ethylene-water), and sp(3)- (methane-water) hybridized intermolecular C-H...O and C-D...O hydrogen bonds has been analyzed at the HF/6-31++G level by using the multicomponent molecular orbital method, which directly takes account of the quantum effect of proton/deuteron. In the acetylene-water case, the elongation of C-H length due to the formation of the hydrogen bond is found to be greater than that of C-D. In contrast to sp-type, the contraction of C-H length in methane-water is smaller than that of C-D. After the formation of hydrogen bonds, the C-H length itself in all complexes is longer than C-D and the H...O distance is shorter than D...O, similar to the GIE of conventional hydrogen bonds. Furthermore, the exponent (alpha) value is decreased with the formation of the hydrogen bond, which indicates the stabilization of intermolecular C-H...O hydrogen bonds as well as conventional hydrogen bonds. In addition, the geometric difference induced by the H/D isotope effect of the intramolecular C-H...O hydrogen bond shows the same tendency as that of intermolecular C-H...O. Our study clearly demonstrates that C-H...O hydrogen bonds can be categorized as typical hydrogen bonds from the viewpoint of GIE, irrespective of the hybridizing state of carbon and inter- or intramolecular hydrogen bond.
通过使用多组分分子轨道方法，在HF/6-31++G水平上分析了sp-（乙炔-水）、sp(2)-（乙烯-水）和sp(3)-（甲烷-水）杂化的分子间C-H...O和C-D...O氢键的几何同位素效应（GIE），该方法直接考虑了质子/氘核的量子效应。在乙炔-水的情况下，发现由于氢键形成导致的C-H长度伸长大于C-D的伸长。与sp型相反，甲烷-水中C-H长度的收缩小于C-D的收缩。形成氢键后，所有配合物中C-H长度本身都长于C-D，且H...O距离短于D...O，这与传统氢键的GIE相似。此外，指数（α）值随着氢键的形成而降低，这表明分子间C-H...O氢键以及传统氢键的稳定性。另外，分子内C-H...O氢键的H/D同位素效应引起的几何差异与分子间C-H...O的几何差异表现出相同的趋势。我们的研究清楚地表明，从GIE的角度来看，C-H...O氢键可被归类为典型氢键，而与碳的杂化状态以及分子间或分子内氢键无关。
