Calculation of Potential Energy Surfaces for HCO and HNO Using Many-Body Methods

The study of microsolvation provides a deeper understanding of solvent effects on reaction dynamics. Here, the properties of the SN2 reaction of hydrated chloride with methyl iodide are investigated by direct dynamics simulations, and how the solute–solvent interactions and the basicity of nucleophiles can profoundly affect the atomic level dynamics is discussed in detail. The results show that the direct-rebound mechanism dominates the substitution reaction, and the roundabout mechanism, which prevails in the indirect unsolvated counterpart reaction, still accounts for a high proportion of the indirect mechanisms. The involvement of a solvent water molecule does not significantly reduce the cross section and rate constant compared to the unhydrated reaction at high collision energy. By varying solvated Cl– to F–, the dominant mechanisms are totally different and in contrast, the dynamics of water does not show much difference, and the departure of H2O tends to occur prior to the substitution reaction because of the facile breakage of the hydrogen bond at high collision energy.

Section: Methodsmentioning

confidence: 99%

Dynamics of Cl^–(H₂O) + CH₃I Substitution Reaction: The Influences of Solvent and Nucleophile

Liu

et al. 2019

“…Bimolecular nucleophilic elimination and substitution of F − + CH 3 CH 2 I were investigated at different levels of theory. All of the critical structures were fully optimized using MP2 19,20 and various density functional theory (DFT) 21−24 methods, that is, CAM-B3LYP, M06-2X, BhandH, B3LYP, and M06, combined with the ECP/d basis set. To test the effect of basis sets, another basis set ECP/t was also used for MP2 and CAM-B3LYP calculations.…”

Section: Methodsmentioning

confidence: 99%

Competing E2 and S_N2 Mechanisms for the F^– + CH₃CH₂I Reaction

Zhang

Xie

et al. 2017

Anti-E2, syn-E2, inv-, and ret-S2 reaction channels for the gas-phase reaction of F + CHCHI were characterized with a variety of electronic structure calculations. Geometrical analysis confirmed synchronous E2-type transition states for the elimination of the current reaction, instead of nonconcerted processes through E1cb-like and E1-like mechanisms. Importantly, the controversy concerning the reactant complex for anti-E2 and inv-S2 paths has been clarified in the present work. A positive barrier of +19.2 kcal/mol for ret-S2 shows the least feasibility to occur at room temperature. Negative activation energies (-16.9, -16.0, and -4.9 kcal/mol, respectively) for inv-S2, anti-E2, and syn-E2 indicate that inv-S2 and anti-E2 mechanisms significantly prevail over the eclipsed elimination. Varying the leaving group for a series of reactions F + CHCHY (Y = F, Cl, Br, and I) leads to monotonically decreasing barriers, which relates to the gradually looser TS structures following the order F > Cl > Br > I. The reactivity of each channel nearly holds unchanged except for the perturbation between anti-E2 and inv-S2. RRKM calculation reveals that the reaction of the fluorine ion with ethyl iodide occurs predominately via anti-E2 elimination, and the inv-S2 pathway is suppressed, although it is energetically favored. This phenomenon indicates that, in evaluating the competition between E2 and S2 processes, the kinetic or dynamical factors may play a significant role. By comparison with benchmark CCSD(T) energies, MP2, CAM-B3LYP, and M06 methods are recommended to perform dynamics simulations of the title reaction.

“…The stationary point properties for the reactants, pre-and postreaction complexes, transition states, and products on the F − (H 2 O) + CH 3 I PES are determined using the MP2 44,45 and DFT, 46−49 50,51 is used for the H, C, O, and F atoms. For iodine, the Wadt and Hay effective core potential (ECP) is used for the core electrons and a 3s, 3p basis set for the valence electrons, 52 which is augmented by a dpolarization function with a 0.262 exponent, and s, p, and d diffuse functions with exponents of 0.034, 0.039, and 0.0873, respectively.…”

Section: Methodsmentioning

confidence: 99%

Electronic Structure Theory Study of the Microsolvated F^–(H₂O) + CH₃I S_N2 Reaction

Zhang

Sheng

2016

The potential energy profile of microhydrated fluorine ion reaction with methyl iodine has been characterized by extensive electronic structure calculations. Both hydrogen-bonded F(-)(H2O)---HCH2I and ion-dipole F(-)(H2O)---CH3I complexes are formed for the reaction entrance and the PES in vicinity of these complexes is very flat, which may have important implications for the reaction dynamics. The water molecule remains on the fluorine side until the reactive system goes to the SN2 saddle point. It can easily move to the iodine side with little barrier, but in a nonsynchronous reaction path after the dynamical bottleneck to the reaction, which supports the previous prediction for microsolvated SN2 systems. The influence of solvating water molecule on the reaction mechanism is probed by comparing with the influence of the nonsolvated analogue and other microsolvated SN2 systems. Taking the CCSD(T) single-point calculations based on MP2-optimized geometries as benchmark, the DFT functionals B97-1 and B3LYP are found to better characterize the potential energy profile for the title reaction and are recommended as the preferred methods for the direct dynamics simulations to uncover the dynamic behaviors.