Tautomerism of monochalcogenosilanoic acids CH3Si(O)XH (X = S,Se, Te) in the gas phase and in the polar and aprotic solution: An ab initio computational investigation |
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Authors: | Qiang‐Gen Li Chao Deng Yi Ren Ning‐Bew Wong San‐Yan Chu Xin Wang |
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Affiliation: | 1. College of Chemistry, Sichuan University, Chengdu 610064, People's Republic of China;2. Key State Laboratory of Biotherapy, West China Medical College, Sichuan University, Chengdu 610041, People's Republic of China;3. Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan;4. Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong |
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Abstract: | Computational investigations by an ab initio molecular orbital method (HF and MP2) with the 6‐311+G(d,p) and 6‐311++G(2df, 2pd) basis sets on the tautomerism of three monochalcogenosilanoic acids CH3Si(?O)XH (X = S, Se, and Te) in the gas phase and a polar and aprotic solution tetrahydrofuran (THF) was undertaken. Calculated results show that the silanol forms CH3Si(?X)OH are much more stable than the silanone forms CH3Si(?O)XH in the gas‐phase, which is different from the monochalcogenocarboxylic acids, where the keto forms CH3C(?O)XH are dominant. This situation may be attributed to the fact that the Si? O and O? H single bonds in the silanol forms are stronger than the Si? X and X? H single bonds in the silanone forms, respectively, even though the Si?X (X = S, Se, and Te) double bonds are much weaker than the Si?O double bond. These results indicate that the stability of the monochalcogenosilanoic acid tautomers is not determined by the double bond energies, contrary to the earlier explanation based on the incorrect assumption that the Si?S double bond is stronger than the S?O double bond for the tautomeric equilibrium of RSi(?O)SH (R?H, F, Cl, CH3, OH, NH2) to shift towards the thione forms [RSi(?S)OH]. The binding with CH3OCH3 enhances the preference of the silanol form in the tautomeric equilibrium, and meanwhile significantly lowers the tautomeric barriers by more than 34 kJ/mol in THF solution. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 |
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Keywords: | ab initio monochalcogenosilanoic acids tautomerism polar and aprotic solution the combined supramolecular/continuum method |
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