Computational Insights into S_N2 and Proton Transfer Reactions of CH₃O⁻ with NH₂Y and CH₃Y

Abstract

Bimolecular nucleophilic substitution (SN2) reactions have been extensively studied in both theory and experiment. While research on C‐centered SN2 reactions (SN2@C) has been ongoing, SN2 reactions at neutral nitrogen (SN2@N) have received increased attention in recent years. To recommend methods for dynamics simulations, the comparison for the properties of the geometries, vibrational frequencies, and energies is done between MP2 and six DFT functional calculations and experimental data as well as the high‐level CCSD(T) method for CH3O‐ + NH2Cl/CH3Cl reactions. The relative energy diagrams at the M06 method for CH3O‐ with CH3Y/NH2Y reactions (Y = F, Cl, Br, I) in the gas and solution phase are explored to investigate the effects of the leaving groups, different reaction centers, and solvents. We mainly focus on the computational of inv‐SN2 and proton transfer (PT) pathways. The PT channel in the gas phase is more competitive than the SN2 channel for N‐center reactions, while the opposite is observed for C‐centered reactions. Solvation completely inhibits the PT channel, making SN2 the dominant pathway. Our study provides new insight into the SN2 reaction mechanisms and rich the novel reaction model in gas‐phase organic chemistry.

Mechanistic Insights into the Proton Transfer and Substitution Dynamics of N-Atom Center Reactions: A Study of CH3O– with NH2Cl

“…Figure S3 provides a trajectory description of the atomistic dynamics of this mechanism. Typically, this mechanism displays a strong directionality characteristic, which always occurs when CH 3 O – initially attacks the front side of NH 2 Cl (the Cl side) and becomes trapped in a potential well with a halogen-bonded complex CH 3 O – –Cl–NH 2 , with an energy of −17.0 kcal/mol with the MP2/aug-cc-pVDZ method for approximately 300 fs. They can then overcome a transition state with an energy of −1.9 kcal/mol to form a hydrogen-bonded prereaction complex CH 3 O – –HNHCl.…”

“…Typically, this mechanism displays a strong directionality characteristic, which always occurs when CH 3 O – initially attacks the front side of NH 2 Cl (the Cl side) and becomes trapped in a potential well with a halogen-bonded complex CH 3 O – –Cl–NH 2 , with an energy of −17.0 kcal/mol with the MP2/aug-cc-pVDZ method for approximately 300 fs. They can then overcome a transition state with an energy of −1.9 kcal/mol to form a hydrogen-bonded prereaction complex CH 3 O – –HNHCl. This mechanism reveals that at the entrance channel, the interaction between the O–Cl bonds is stronger than that of the O–N bonds and lasts for a certain time (∼300 fs), as reflected by their bond lengths (Figure S4).…”

“…We previously compared stationary points obtained employing the MP2 method and various DFT functionals, as well as the high-level CCSD(T)/ CBS method, and recommended the adoption of the MP2 method for dynamical simulations. 51 To economize computational resources, the MP2/6-311G** 54−56 level was employed for propagating trajectories for the CH 3 O − + NH 2 Cl reaction. As mentioned, the quasi-classical sampling approach was utilized to acquire the initial coordinates and momenta for the trajectories, with ZPE taken into consideration.…”

“…Chemical dynamics simulations for the CH 3 O – + NH 2 Cl reactions were conducted utilizing the VENUS dynamics program linked with the NWChem electronic structure program, with the movement of atoms throughout the reaction path being monitored. We previously compared stationary points obtained employing the MP2 method and various DFT functionals, as well as the high-level CCSD­(T)/CBS method, and recommended the adoption of the MP2 method for dynamical simulations . To economize computational resources, the MP2/6-311G** − level was employed for propagating trajectories for the CH 3 O – + NH 2 Cl reaction.…”

“…Schematic representation of the potential energy profiles depicting stationary points along PT (black) and S N 2 (pink) channels for (a) CH 3 O – + NH 2 Cl reaction and (b) F – + NH 2 Cl reaction with MP2/aug-cc-pVDZ level in the top line and CCSD­(T)/CBS level in the parentheses of the bottom . The numbers indicate classical energies in kcal mol –1 without a zero-point energy (ZPE).…”