Theoretical Investigation on Hydrogen Abstraction by NO₂ from Symmetric Ethers (CH₃)_2xO (x = 1–4)

Abstract

Hydrogen abstractions by NO from symmetric ethers are investigated to determine the rate constants and explore the effect of the functional group on rate constants at different reaction sites. The involved ethers are dimethyl ether (DME), diethyl ether (DEE), dipropyl ether (DPE), and dibutyl ether (DBE). The B3LYP method with a 6-31G(2df,p) basis set is employed to optimize the ground-state geometries and for frequency and intrinsic reaction coordinate calculations. The G4 method is used to calculate the electronic energies for the small ethers (DME and DEE). Given the heavy computational cost of the G4 method, the modified G4MP2 method is applied for larger ethers (DPE and DBE) and also for DME to verify the accuracy of the G4MP2 method by benchmarking with the G4 method. The high-pressure limit rate constants are calculated within the temperature range of 500-2000 K, with the asymmetrical Eckart tunneling correction as well as one-dimensional hindered rotor treatment. The calculated rate constants agree well with the literature data, and the branch ratio analysis suggests that the cis-HONO channel basically dominates the hydrogen abstraction reactions and shows a decrease at high temperatures, followed by HNO and trans-HONO channels; in addition, the hydrogen abstraction at the C site adjacent to the ether bond (α reaction site) accounts for most of the reactions. Furthermore, the total rate constants of the ethers are compared to those of their half-structurally alkanes, and linear Bell-Evans-Polanyi correlations are observed.

Symmetric Ethers as Bioderived Fuels: Reactivity with OH Radicals

“…The model by Thion et al anticipates an even stronger reactivity enhancement, with the δ channel being more important than the γ channel. The recent theoretical work from Shang et al showed similar trends in the branching ratios for the abstraction reactions of dialkyl ethers by NO 2 . Interestingly, the SAR approach, as shown by the dotted lines in Figure , performs remarkably well in predicting the branching ratios, though it is unable to capture the reactivity order previously mentioned for the secondary sites in DBE: α > γ > β.…”

“… a The data are compiled from Luo, Zhou et al, Shang et al, Yang et al, Serinyel et al, Thion et al., and Cai et al …”

“…The rate parameters were taken as analogous to the C−H primary sites of n-alkane + OH reactions as given by Sivaramakrishnan and Michael. The data are compiled from Luo, 40 Zhou et al, 29 Shang et al, 41 Yang et al, 42 Serinyel et al, 10 comparable branching ratios but with a slight T dependence. In line with Cai et al, 5 we observed that the contribution of the α(2°) channel decreases with increasing alkyl chain length in dialkyl ethers and thus an increase in the number of sites where hydrogen atoms can be abstracted.…”

Advanced kinetic calculations with multi-path variational transition state theory for reactions between dimethylamine and nitrogen dioxide in atmospheric and combustion temperature ranges

“…Since the energies of TSs are much higher than that of reactants, the formation of RCs with well depths of <3 kcal mol −1 is not a dominant process, which can be neglected in the rate constant calculations. 43 Fig. 9 compares the calculated MP-CVT/SCT rate constants of different channels for the H-abstraction reactions DMA + NO 2 .…”

“…DMA has two types of hydrogen atoms, and the H-abstraction reactions from DMA by NO 2 at N-site and C-site are denoted as R1 and R2, respectively. According to the available studies, 43,44 the H-abstraction reactions by NO 2 lead to three products, i.e., HNO 2 , cis-HONO, and trans-HONO, and these channels are denoted as Rxa, Rxb, and Rxc (x = 1 and 2), respectively. In addition, 7 different reaction channels are also identified in this work.…”