Chemical Dynamics Simulations On The Bimolecular Nucleophilic Substitution And Proton Transfer Reactions Of OH^- With NH₂Cl

Bimolecular nucleophilic substitution（S_N2）reaction plays an important role in chemistry and biochemistry;in particular,the nitrogen-centered S_N2 reaction is crucial for organic synthesis and the treatment of cancer.A fuller comprehension of the microscopic processes involved in this reaction can be gained by dynamic studies at the atomic level.At present,there is limited research on the dynamics of OH^-+NH₂Cl reaction,especially the microscopic mechanism of S_N2 competes with proton transfer reaction（PT）.In this paper,the OH^-+NH₂Cl reaction is mainly studied from the potential energy surface and dynamics,and compared with the F^-+NH₂Cl and OH^-+CH₃Cl reactions.The bimolecular nucleophilic substitution and proton transfer reactions of the OH^-+NH₂Cl reaction are expressed by various electronic structure calculation methods.Both the backside attack of bimolecular nucleophilic substitution and proton transfer reaction are exothermic,and the stationary points of the potential energy surface（PES）are below the reactant asymptote.In general,the potential energy surface is similar to the bimolecular nucleophilic substitution reaction with the C-centered.The hydrogen-bonded complex N---HOH/NH---Cl has discovered on both sides of the transition state barrier in the OH^-+NH₂Cl system,despite the absence of an ion-dipole complex present.In addition,a halogen-bonded complex（HO^---ClNH₂）and two hydrogen-bonded complexes（HONH₂---Cl^-and Cl^----HONH₂）are also found.By comparing the energies optimized by the MP2/aug-cc-p VDZ method with the benchmark energies CCSD（T）/CBS,it is discovered that the MP2/aug-cc-p VDZ approach has a good consistency,and this method is selected for the direct dynamics simulation.Direct dynamics simulations are conducted on the OH^-+NH₂Cl reaction at collision energies of 300 K and 40 kcal mol^-1.Two product channels of S_N2 and PT,NH₂OH+Cl^-and H₂O+NHCl^-,are observed.By evaluating the reaction likelihood and branching ratio for various collision energies,it can be determined that PT is more likely to occur and that it dominates the reaction.The simulation results show that reactions undergo both direct and indirect mechanisms.At low energies,the reaction is dominated by the indirect mechanism of hydrogen-bonded complex,while at high energies,the direct stripping mechanism mainly occurs.This is different from the reaction with nucleophile F^-,which is dominated by the indirect mechanism at high energies.And further examine the aforementioned reaction process from the distribution of scattering angle and product energy.The dynamics results obtained from the study of the OH^-+NH₂Cl reaction can provide some reference for the experiment and provide theoretical supplements for the experimental results.