Reaction-Path and Dual-Level Dynamics Calculations of the CH₃F + OH Reaction

Abstract

Using two approaches, reaction-path dynamics (which uses information on electronic structure energy and energy derivatives calculated ab initio along the minimum energy path) and dual-level dynamics (in which the reaction-path is calculated at a low level of theory, and stationary point information from a high level of theory is used to interpolate corrections to energy quantities, vibrational frequencies, and moments of inertia), the reaction-path for the CH3F + OH reaction was traced. Qualitatively, both methods yield similar results, showing the usefulness of the more economical dual-level approach. The H2O product may be vibrationally excited due to the nonadiabatic flow of energy between the reaction coordinate and the O−H bound mode. The rate coefficents were calculated for the temperature range 200−1000 K using the variational transition-state theory. The tunneling effect was included in the first approach using the small-curvature tunneling method, and in the second using the microcanonical optimized multidimensional tunneling method. Tunneling plays an important role in this reaction and the calculated rate coefficients show a more pronounced curvature in the Arrhenius plot than the experimental data.

Comparison of Free-Energy Methods to Calculate the Barriers for the Nucleophilic Substitution of Alkyl Halides by Hydroxide

“…Nucleophilic substitution, having equation X − + RY → RX + Y − where X = halide, R = alkyl group and Y = leaving group, is an extensively studied reaction, [25][26][27][28][29][30] via a single transition state with a concerted ligand switch. Most theoretical studies have been in the gas phase, 25,26 others in implicit solvent, 27,28 and more recent studies in explicit solvent. 31,32 We employ four different Hamiltonians and three free-energy methods.…”

“…We compare implicit-solvent QM and explicit-solvent QM/MM methods to determine the reaction kinetics for the model reaction of bimolecular nucleophilic substitution of alkyl halides reacting with hydroxide in water. Nucleophilic substitution, having equation X – + RY → RX + Y – where X = halide, R = alkyl group, and Y = leaving group, is an extensively studied reaction, − via a single transition state with a concerted ligand switch. Most theoretical studies have been in the gas phase, , others in implicit solvent, , and more recent studies in explicit solvent. , We employ four different Hamiltonians and three free-energy methods.…”

Computational study on OH radical reaction with CHF2CHFCHF2(HFC‐245ea) between 200 and 400 K

“…Transition state theory (TST), ab initio methods, and density functional theories (DFT) can also be used to compute the rate coefficients of these reactions. Kinetics of these reactions with several HFCs were reported in the literature using these computational methods 5–20.…”

Static and dynamic reaction pathways involved in the reaction of O− and CH3F

“…The reactions involving methyl fluoride (CH 3 F) have attracted much attention because of their important roles in atmospheric chemistry and combustion chemistry [1][2][3][4][5][6][7]. As CH 3 F is a typical polar molecule, the reaction between CH 3 F and a nucleophile probably undergoes a process of the bimolecular nucleophilic substitution (S N 2) reaction, e.g.…”