Dynamic Investigations Of Several Important Chemical Reactions

The core content of chemistry is inseparable from chemical reactions.The research of chemical reactions involves complex reaction mechanisms.Dynamic simulation is an important method to study reaction mechanism from the microscopic level.Dynamic method is used for theoretical simulation investigations on three important chemical reactions in this thesis.Rich and important dynamics information were obtained to help people further understand the nature of chemical reactions at the microscopic level.The first reaction system in this thesis is OH+H₂O reaction.This symmetric reaction OH+H₂O→H₂O+OH is very important in the atmosphere,combustion,interstellar media,and the environment,and has been studied extensively.About 48000points were sampled and calculated at the level of CCSD（T）-F12a/AVTZ.Then the full dimensional accurate potential energy surface（PES）of this reaction system was built by using the permutation invariant polynomial-neural network（PIP-NN）method,the root mean squared error（RMSE）is 0.12 kcal·mol^-1.Base on the accurate PES,the quasi-classical trajectory（QCT）method was employed to study the dynamics of this reaction system.The integral cross section（ICS）and differential cross section（DCS）were determined.It has been found that the integral cross section was increased gradually as a function of the collision energy ranging from 8 to 30 kcal·mol^-1.Besides,at a collision energy of 20 kcal·mol^-1,the dynamics simulation results show that the OH moiety can be considered as a spectator.The differential cross section（DCS）was dominated by backward scattering,and there were some contributions from sideway scattering,it’s not ignored.These results are consistent with the tripping mechanism and direct rebound mechanism.In addition,the reaction reactivity was studied at with different excitations in the reactant vibration and rotation states,then have a deeper understanding of the reaction mechanism.The second reaction system in this thesis is the reaction between butadienes and allyl cations.This reaction has been studied extensively in synthesis.For example,this reaction provides a straightforward process to the sesquiterpene artemisinin.A selectivity model has been proposed based on quantum chemical calculation.The results showed that the widths of pathways to products can be much more essential than the barrier height.Namely,there is an entropic effect,which has always been neglected but should be of importance in developing useful selectivity models and in designing new selective reactions.The transition state,minima,and minimum energy pathways（MEP）have been calculated and analyzed by using the density functional theory（DFT）computations.The variational transition state theory（VTST）was employed to calculate the reaction path to explore the role of entropic effect on the product selectivity.By using the Progdyn script,the quasi-classical trajectory（QCT）and classical trajectory methods were used in the uphill and downhill ab initio molecular dynamics simulations.In addition,the non-statistical dynamic effects were analyzed to see if they affect the reaction selectivity.In order to explore how the shape of the PES affects the selectivity of the reaction,the reduced-dimensional potential energy surface（reduced-PES）was determined by the relaxed scan.The third reaction system in this thesis is the reaction between phenyl vinyl sulfoxide and dichloroketene.Explore the reaction dynamics which involved in the post-transition-state bifurcation（PTSB）.Based on early experimental conclusions,we proposed a possible reaction path,and analyzed the transition state,minima and reaction coordinates on the proposed path by using the density functional theory.During the process of the reaction,it was found that the reaction may involve the process of post-transition-state bifurcation（PTSB）,which related to the selectivity of the reaction.The final product is butyro-lactone,in which the oxygen of the C-O single bond may come from different components.One possible source is the dichloroketene,another from vinyl sulfoxides.In order to explore the formation process of products,the direct molecular dynamics simulation was used to perform downhill quasi-classical dynamics calculations from the bifurcation transition state TSS1.The dynamic simulation calculation discovered the source of oxygen atoms in the C-O single bond on the butyro-lactone product and the selectivity of the reaction.