水与三甲基硅烷醇羟基的氢同位素交换反应的理论研究

以(CH_3)_3SiOH羟基模拟Li_4SiO_4陶瓷表面羟基,研究了H_2O与(CH_3)_3SiOH羟基H的氢交换反应机理.采用HF, MP2方法,在3-21G和6-311G++H~(**)水平上优化了(CH_3)_3SiOH, H_2O, (CH_3)_3SiOH-H_2O复合物及氢交换反应过渡态的结构.计算了生成(CH_3)_3SiOH-H_2O复合物的反应热,探讨了氢交换反应的路径.结果表明,可以形成2种形式的(CH_3)_3SiOH-H_2O复合物,一种是H_2O的O原子与(CH_3)_3SiOH羟基的H原子作用形成的复合物,另一种是H_2O的H原子与(CH_3)_3SiOH羟基的O原子作用形成的复合物.MP2/6-311G++~(**)水平上,对基组重叠能(BSSE)进行校正后,上述2种复合物的反应热分别为20.046 5 kJ/mol和21.630 7 kJ/mol.有利的氢交换反应路径为:H_2O的H原子与(CH_3)_3SiOH羟基的O原子作用形成的复合物,然后H2O提供1个H原子、1个O原子,(CH_3)_3SiOH提供1个O原子、1个Si原子形成由O, H, O, Si 4个原子构成的四元环过渡态,最后H_2O的O原子与(CH_3)_3SiOH 的Si原子成键形成新的(CH_3)_3SiOH,而(CH_3)_3SiOH的Si-O键断裂,由(CH_3)_3SiOH的羟基和H_2O的1个H原子形成新的H_2O分子,MP2/6-311G++~(**)水平上,BSSE校正后,此路径的反应活化能为186.898 4 kJ/mol.

Ab Initio Study on the Mechanism of Hydrogen Exchange Reaction Between H_2O and Hydroxyl of (CH_3)_3SiOH

The hydrogen exchange reaction mechanism between H_2O and -OH of surface of Li_4SiO_4 ceramic has been investigated using hydroxyl of (CH_3)_3SiOH as a simple model of hydroxyl of surface of Li_4SiO_4 ceramic. The structures of (CH_3)_3SiOH, H_2O, (CH_3)_3SiOH-H_2O complexes and transition states of hydrogen exchange reaction have been optimized at HF/3-21G, HF/6-311G++~(**), and MP2/6-311G++~(**) levels. The association energies of (CH_3)_3SiOH-H_2O and the path of hydrogen exchange reaction have also been explored. The results show that two of associate complexes can be formed, the O of H_2O interact with the H of hydroxyl of (CH_3)_3SiOH to form one complex and the another complex is formed by the interaction between the H of H_2O and the O of hydroxyl of (CH_3)_3SiOH. At HF/6-311G++~(**) and MP2/6-311G++~(**) levels, the association energies after basis set superposition error correction of two complexes above are 18.016 1, 18.816 6, 20.046 5, 21.630 7 kJ/mol, respectively. The favorable path of hydrogen exchange reaction is as follow: first, the H of H_2O interactes with the O of hydroxyl of (CH_3)_3SiOH to form associate complex, second, 4-membered ring transition state consisted of O, from H_2O, H, from H_2O, O, from (CH_3)_3SiOH, Si, from (CH_3)_3SiOH is formed, third, the formation of new O-Si bond and the break old O-H bond lead the new (CH_3)_3SiOH to be formed, at the same time, the new H_2O is formed resulting in the rupture of old O-Si bond and the formation of new H-O bond. At HF/6-311G++_(**) and MP2/6-311G++~(**) level, the activation energies of this path are 232.905 3 kJ/mol and 186.898 4 kJ/mol with counterpoise correction.