Quantum Chemistry Study On The Reaction Of Singlet Alkylidenecarbenes With Oxirane, Thiirane And Methanol

In this paper, high-level quantum chemistry calculation methods are used to theoretically investigate on the potential energy surfaces of some alkylidenecarbenes with oxirane, thiirane, methanol and the abstraction reactions of germylene with thiirane and oxirane. Much kinetic information of these reactions was obtained. The results presented in this paper may be very helpful for understanding the reactions of active intermediate and may provide some elemental theoretical basis for futher experiments on active intermediate reactions. The whole paper consists of six chapters.Chapter 1 mainly reviews the evolution of alkylidenecarbenes and germylenes reactions. The second chapter summarizes the theory of quantum chemistry and calculation methods of this paper.In the third chapter, the mechanisms for the abstraction reactions of alkylidenecarbenes with oxirane have been characterized in detail by density functional theory. The results show that the electro negativity of the substituents played an important role to predict its activity for the abstraction reactions. The major conclusion was that the stronger the p-donation or the more electronegative the substituents were, the smaller theâ–³E_ST of XYC=C: and the lower the activation energy for the abstraction reactions. In other words, it is the electronic factors, rather than the steric ones, that play a decisive role in the chemistry of the alkylidenecarbene species.In the fourth chapter, the mechanisms for the abstraction reactions of alkylidenecarbenes with thiirane have been characterized in detail using density functional theory. The results show that the electro negativity of the substituents played an important role to predict its activity for the abstraction reactions. The major conclusion showed: the more strong the p-donation or the more electro negativity the substituents were the smaller theâ–³E_ST of XYC=C and the lower the activation energy for the abstraction reactions. In the other words, it is the electronic factors, rather than the steric factors, that play a decisive role in the chemistry of the alkylidenecarbene species. Furthermore, a comparison with oxirane led also to the same result.In the fifth chapter, the mechanisms for the insertion reactions of alkylidenecarbenes with CH₃O-H have been investigated at the B3LYP/6-311G (d, p) level of the theory. According to our model calculations these insertion reactions will easily yield vinyl ether products and for a given single substituted alkylidenecarbene will yield cis-/trans- isomer mixture. Moreover the reactivity of alkylidenecarbene decreases in the order: HFC=C > HC1C=C > HBrC=C> H(CH₃)C=C> H₂C=C.In the sixth chapter, the potential energy surfaces for the abstraction reactions ofgermylene with thiirane have been characterized in detail using deasity functional theory (DFT). The major conclusion is as follow: the reactions are in two steps: (1) germylenes and thiirane form an intermediate complex through exothermal reactions without any barrier; (2) the intermediate complexes isomerize to give the products. Furthermore, the stronger the p-donation is or the more electronegative the substituents are the bigger theâ–³E_ST of X₂Ge, The higher the action energy for the abstraction reactions will be.