Direct dynamics study on the reaction of acetaldehyde with ozone

Abstract

The hydrogen abstraction reaction of ozone with acetaldehyde has been studied theoretically over the temperature range 250-2500 K. Two different reactive sites of acetaldehyde molecule, CH(3) and CHO groups have been investigated, and results confirm that the CHO group is a highly reactive site. In this study, the geometries and harmonic vibrational frequencies of all stationary points are calculated at the MPW1K, BHandHLYP, and MPWB1K levels of theory. The minimum energy paths (MEPs) were obtained at the MPW1K/6-31+G(d,p) level of theory. To refine the energies along the MEPs of each channel, single-point energy calculations were performed by a higher-level energy calculation method (denoted as HL). The rate constants were evaluated based on the MEPs from the HL method in the temperature range 250-2500 K by using the conventional transition state theory (TST), the canonical variational transition state theory (CVT), the microcanonical variational transition state theory (muVT), the CVT coupled with small-curvature tunneling (SCT) correction (CVT/SCT), and the muVT coupled with Eckart tunneling correction (muVT/Eckart). The fitted three-parameter Arrhenius expressions of the calculated CVT/SCT and muVT/Eckart rate constants of the H abstraction from CHO group are k CVT/SCT(T) = 4.92 x 10(-27).T 3.77.e(-7867.0/T) and k muVT/Eckart(T) = 2.10 x 10(-27).T(3.90).e(-7706.2/T), respectively. The fitted three-parameter Arrhenius expressions of the calculated CVT/SCT and muVT/Eckart rate constants of the H abstraction from CH3 group are k(CVT/SCT)(T) = 1.27 x 10(-27).T(3.94).e(-14554.1/T) and k muVT/Eckart(T) = 1.62 x 10(-26).T(3.66).e(-15459.8/T), respectively.

H-Atom Abstraction Reactions by Ground-State Ozone from Saturated Oxygenates

“…More generally, a number of studies have investigated the mechanisms and kinetics of ozone reacting with unsaturated oxygenates, − acetaldehyde, fluorocarbons, methane, formaldehyde, , unsaturated ketones, and alkyl hydroperoxides, , and summaries of atmospheric reaction mechanisms in the troposphere are available in a recent review . However, despite these experimental studies, there is a dearth of theoretical calculations for the reactions of systems larger than H 2 CO + O 3 , which is probably due to the intrinsic multireference character of ozone …”

Theoretical study on the atmospheric transformation mechanism of pirimiphos-methyl initiated by O3

“…Comparing these seven channels, abstractions of H 20 and H 22 have lower barriers and require lower reaction heats. The energy barriers of these two H-abstraction reactions by O 3 molecules are lower than for alkanes or aldehydes (Timerghazin et al, 1999;Yang et al, 2008;Voukides et al, 2009). Moreover, DG for the H 20 and H 22 abstraction processes is less than zero, while for other processes it is larger than zero, as shown in Tables 1 and S1.…”

“…Studies have shown that ozonation of the CH bond in saturated hydrocarbons initiates with H abstraction by O 3 , followed by the formation of an R Å Å OOOH radical pair (Cerkovnik et al, 2002;Yang et al, 2008;Voukides et al, 2009). Within the structure of PMM, seven different kinds of hydrogen can be abstracted by O 3 , as shown in Fig.…”

“…The calculated free energy (DG) indicates that the carbonylation reaction will be spontaneous once an H atom is abstracted by O 3 . Similar to the N-dealkylation reaction, the carbonylation reaction is also reported as an important atmospheric degradation pathway for pesticides containing N,N-dialkyl groups (Yang et al 2008(Yang et al , 2010Atkinson et al, 1999;Meng et al, 2009). Since the decomposition of the intermediate IM2 also involves a pericyclic proton-transfer process, the reaction energy barrier may again be reduced with the assistance of water.…”

Kinetic study on the linalool ozonolysis reaction in the atmosphere

“…16,17 The geometrical parameters of stationary points are optimized at the MPWB1K/6-31+G(d,p) level. The vibrational frequencies were calculated at the same level to determine the nature of the stationary points.…”