Theoretical Study Of The Mechanism Of The Gas-phase Anion Molecule Reaction

Gas-phase anion molecule reaction plays an important role in discovering the reaction mechanisms of the new synthetic and measuring some important thermochemical values because they are in general rapid, intense and selective. Especially, gas-phase anion molecule reaction was developed greatly during the past several decades for the improvement of experimental technique and test method. And numerous papers about the experiment were published. In contrast to these experimental studies, there were only a few theoretical studies on the reactions of gas phase anion chemistry with many channels and steps. So three typical reactions (allyl anion with N₂O and allenyl anion with CS₂ and COS) which were carried out by Charles were selected as the object of study.In the paper, on the basis of the molecular orbital theory, the tradition transition state theory as well as quantum chemistry theory, the selected systems have been investigated using Moller-Plesset perturbation theory (MP2), the coupled cluster CCSD(T) calculations and the Natural Bond Orbital analysis. The structures of the intermediates and the transition states along the reaction paths were fully optimized. The spectrum datum, the thermodynamic datum were all used to obtain the potential surface. The information of orbitals was also used to explain the reaction mechanism.The whole paper consists of five chapters. Chapter 1 is mainly about the development and application of quantum chemistry and the characteristics of organic gas-phase anion molecule reaction are also concerned. In Chapter 2, we will introduce the theory and computation methods that we based on.In Chapter 3, the gas-phase reaction mechanism of allyl anion with N₂O has been investigated at the MP2/6-31G(d, p) level of the theory. The single-point energies have also been refined at the CCSD(T)/6-31G(d, p) level to get more accurate energies using the MP2/6-31G(d, p) optimized geometries. The computational results indicate that the reaction involves three reaction pathways to produce cis-vinyl-diazomethyl anion, trans-vinyl-diazomethyl anion and allenyl anion. The two channels which produce cis-vinyl-diazomethyl anion and trans -vinyl-diazomethyl anion are the major competition channels of the reaction. The rate coefficients of the rate-determining step of all the reaction channels have also been carried out using statistic thermodynamics and conventional transition state theory at the normal temperature (298K).In Chapter 4, the mechanism for the gas-reactions of the allenyl anion with CS₂ has been characterized in detailed at the MP2/6-31++G(d, p) level of the MP2 theory. The main product thioketenyl anion will be formed via a series of cyclization, rearrangement and elimination. The calculations show that the major product channel is the direct dissociation of IM4.In Chapter 5, a same investigation has been taken for the reaction of allenyl anion with COS. This reaction is complicated by the fact that after the initial addition of COS to the allenyl anion, cyclization can occurs either through the oxygen or the sulfur atom and contains a series of cyclization, rearrangement and elimination. As a result, the thioketenyl anion and four-membered ring intermediate IM5 are the main products.