Quantum Chemical Study On The Abstraction Reaction Of Alkylidenesilylene And Alkylidenegermylene With Oxirane And Thiirane

This paper respectively takes the abstraction reactions from oxirane and thiirane by silylidene and germylidene as model reactions to investigate the reaction mechanisms of these abstraction reactions, which aims at revealing the reaction mechanisms of the abstraction reactions from oxirane and thiirane by unsaturated silylene and unsaturated germylene compounds.The main methods used in this paper are B3LYP and MP2 theories of quantum chemistry implemented in the Gaussian 98, which have respectively been employed to locate all the stationary points along the reaction pathways at the level of 6-311G(d, p). Full optimization and vibrational analysis are done for the stationary points on the reaction profile. Zero-point energy and CCSD(T) corrections are included for energy calculations. In order to explicitly establish the relevant species, IRC is also calculated for all the transition states appearing on the cycloaddition energy surface profile.By studying on the mechanisms of abstraction reactions of alkylidenesilylene and alkylidenegermylene with oxirane and thiirane, the results show that (1) the reaction pathways for both two reactions consist of two ways which can yield bent products and ethylene by syn-isomers, three-membered ring products and ethylene by anti-isomers, respectively; (2) the series of reactions consist of two steps (except the reaction 1 of alkylidenesilylene and oxirane): the first one is a barrier-free exothermic reaction, resulting in intermediates, and the second is from intermediates to products through transition states; But in the deoxygenation reaction, one of the breaking C-0 bonds is greatly stretched, whereas in the case of desulfurization, the two breaking C-S bonds are almost equally stretched in the transition structures. That is to say that oxirane undergoes concerted deoxygenation by reaction via an asynchronous transition state. In contrast, thiirane desulfurization reactions are predicted to be concerted but more synchronous; (3) the three-member products can further react with oxirane and thiirane to form the more stable products.The whole paper consists of five chapters. Chapter 1 describes the progeess and application of quantum chemistry as well as the development and the present situation of alkylidenesilylene and alkylidenegermylene. In Chapter 2, introduces elementary theory and quantum chemistry computation methods, which mainly-contained molecular orbit theory, density fouctional theory, tradition transition state theory and the intrinsic reaction coordinate theory. The contents of the two chapters were the basis and background of our studies and offer us with useful and reliable quantum methods.In Chapter 3 and 4, we select the abstraction reactions from oxirane and thiiraneby silylidene and germylidene as model reactions and describe the paths of reaction simply; therefore the mechanisms of abstraction reactions are clear at a glance. This paper not only reveals the existing forms of many new species of silicon and germanium elements and enriches the contents of silicon and germanium elements compounds, but also has important significance to further understand the properties,bonding modes and rules of silicon and germanium elements, which will promote the subject construction of abstraction reactions of unsaturated silylene and unsaturated germylene. The research results will not only provide theoretical chemists with theoretical evidence to further study this topic. In the last Chapter, we select the insertion reaction between alkylidenecarbene and water, and enable us to have a deeper understanding to its element compound.