Ab Initio Study on the Mechanism of Hydrogen Exchange Reaction Between H₂O and Hydroxyl of (CH₃)₃SiOH

The hydrogen exchange reaction mechanism between H2O and －OH of surface of Li₄SiO₄ ceramic has been investigated using hydroxyl of (CH₃)₃SiOH as a simple model of hydroxyl of surface of Li₄SiO₄ ceramic. The structures of (CH₃)₃SiOH, H₂O, (CH₃)₃SiOH—H₂O 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 (CH₃)₃SiOH—H₂O 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 H₂O interact with the H of hydroxyl of (CH₃)₃SiOH to form one complex and the another complex is formed by the interaction between the H of H₂O and the O of hydroxyl of (CH₃)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 H₂O interactes with the O of hydroxyl of (CH₃)₃SiOH to form associate complex, second, 4-membered ring transition state consisted of O, from H₂O, H, from H₂O, O, from (CH₃)₃SiOH, Si, from (CH₃)₃SiOH is formed, third, the formation of new O—Si bond and the break old O—H bond lead the new (CH₃)₃SiOH to be formed, at the same time, the new H₂O 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.