Dual-level direct dynamics studies for the reactions of CH3OCH3 and CF3OCH3 with the OH radical

Abstract

The reactions CH n D 4−n + OH → P and CH 4 + OD → CH 3 + HOD as a test of current direct dynamics computational methods to determine variational transition-state rate constants. I.The reactions of CH 3 OCH 3 ϩOH (R1) and CF 3 OCH 3 ϩOH (R2) via two hydrogen abstraction channels are investigated theoretically using the dual-level direct dynamics approach. The minimum energy path calculation is carried out at the MP2/6-311G(d,p) level, and energetic information is further refined by the G3 theory. For each reaction hydrogen abstraction is favored for the out-of-plane hydrogen, while the abstraction from the in-plane hydrogen is a minor channel. Hydrogen-bonded complexes are present on the reactants and products sides of the primary channel, indicating that the reactions may proceed via an indirect mechanism. By means of variational transition state theory with interpolated single-point energies method the dynamic results of all channels are obtained, and the small-curvature tunneling is included. The total rate constants calculated from the sum of the individual rate constants are in good agreement with the experimental data and are fitted to be k 1 ϭ3.33ϫ10 Ϫ20 T 2.91 exp(Ϫ409.7/T) and k 2 ϭ1.23ϫ10 Ϫ24 T 3.93 ϫexp(Ϫ188.2/T) cm 3 molecule Ϫ1 s Ϫ1 over the temperature range 230-2000 K. The calculation indicates the CH 3 OCH 3 ϩOH reaction may proceed much easier than the CF 3 OCH 3 ϩOH reaction and fluorine substitution decreases the reactivity of the C-H bond.

Theoretical study of the reactions CF3CH2OCHF2 + OH/Cl and its product radicals and parent ether(CH3CH2OCH3) with OH

“…This indicates that the fluorine atom substitution for hydrogen atom on carbon atom reduces the reactivity of CH toward hydrogen abstraction. Similar conclusion can be obtained from the reactions OH with CH 3 OCH 3 and CF 3 OCH 3 37. In addition, for H‐abstraction reaction from CHF 2 group, the barrier heights of channels R 1a (6.68 kcal/mol) and R 2a (3.15 kcal/mol) are lower than those of reactions CF 3 OCHF 2 + OH and CF 3 OCHF 2 + Cl, 7.01 and 6.27 kcal/mol,38 respectively.…”

Multiconformer transition state theory rate constants for the reaction between OH and ‐dimethoxyfluoropolyethers

“…Such reactions take place very frequently in the atmosphere (see Refs [] and [] and references therein), with the case of reaction referring to a reaction between a specific class of ethers and the OH radical. Recent investigations have clarified the mechanistic details of reactions between ethers and OH, with one of the conclusions drawn from these studies being that such reactions share the same type of reaction path of many radical–molecule reactions of atmospheric interest: there is the formation of prereactive complexes (PRC) and product complexes (PC) connected to the hydrogen‐abstraction transition states (TS). Such a reaction path can be outlined in a simple scheme like the one presented Figure , which is adapted for the specific case of HFPEs.…”

Oxidation mechanism of diethyl ether: a complex process for a simple molecule

“…Indeed, a considerable amount of experimental data on the gas phase oxidation of short-chain ethers have been reported in the literature. 7,8 Dimethyl ether (DME) is the most investigated member of the class, from both experimental [9][10][11][12] and theoretical [13][14][15] point of view. Experimental studies also exist on the oxidation of the other short-chain ethers 16 such as diethyl ether (DEE), 6,[17][18][19][20][21][22] diisopropyl ether (DIPE) 19,23 or methyl tert-butyl ether (MTBE) 24 in very different conditions (e.g.…”