OH Radical Gas Phase Reactions with Aliphatic Ethers: A Variational Transition State Theory Study

Abstract

A theoretical study of the mechanism and kinetics of the OH radical reactions with aliphatic ethers is presented. Several methods were evaluated using the 6-311++G(d,p) basis set, with dimethyl ether as a test molecule. On the basis of the dimethyl ether results, the M05-2X functional was selected for the rest of the calculations. All the possible H abstraction paths have been modeled, and the importance of differentiating among H atoms bonded to the same C atom, according to their orientation with respect to the O atom in the ether, is analyzed. The rate coefficients are calculated using interpolated variational transition-state theory by mapping (IVTST-M), within the IVTST-M-4/4 scheme, in conjunction with small-curvature tunneling (SCT) corrections. The discussion is focused on the 280-400 K temperature range, but additional information is provided for an extended range (280-2000 K). Our analysis suggests a stepwise mechanism involving the formation of H bonded complexes in the entrance and exit channels. The vicinity of the O atom was found to increase the relative site reactivity. In fact, it was found to influence reactivity to a larger extent than the nature of the carbon site (primary, secondary, or tertiary). The overall agreement between the calculated and the available experimental data is very good and supports the reliability of the rate coefficients and the branching ratios proposed here for the first time. It also supports the performance of the M05-2X functional and the IVTST-M-4/4 scheme for kinetic calculations.

Daytime Reactions of 1,8‐Cineole in the Troposphere

“…Tables 3 and 4 show the energies of the transition states evaluated at the QCISD(T)/6‐31G* level of theory for the attack of OH and Cl, respectively, at the various CH sites in 1,8‐cineole. Recent theoretical work has shown that the M05‐2X functional reproduces the experimental data available for the reactions of ethers+OH63 better than other methods of calculation.…”

A Theoretical Study on the Antioxidant Activity of Piceatannol and Isorhapontigenin Scavenging Nitric Oxide and Nitrogen Dioxide Radicals

“…M05-2X functional has been chosen as it yields satisfactory overall performance for the thermodynamic and kinetic calculations in organic and biological systems involving free radical reactions [35–37]. Unrestricted wave function was employed for the open-shell system.…”

A quantum chemical study on ˙Cl-initiated atmospheric degradation of acrylonitrile

“…M05-2X has been proven to calculate kinetic data accurately. 50,51 Reliable wavefunction methods such as CCSD(T) can be used to obtain excellent energies, but incur problems from large spin contamination in the transition states at the UCCSD(T) level of theory. In our system, the S 2 values, spin contamination before and aer annihilation, range from 0.92 to 0.77 for IM1 at UCCSD(T)// M05-2X; this rate error is known to result from spin contamination, or the acceptable instrumental error of two experiments.…”