Kinetic Study and Rate Coefficient Calculations of the Reaction of 1-Hydroxyethyl Radical with Nitric Oxide
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The kinetic study of the reaction of 1-hydroxyethyl radicals (CH3CHOH) with nitric oxide (NO) was performed over the temperature range of 200-1100 K and the pressure range of 1.0 × 10-5 to 10.0 bar. The geometries of all of the stationary points were optimized at the B3LYP/6-311++G(df,pd) level of theory, and the energetics were refined at the CCSD(T)/cc-pVTZ level of theory. Eight reaction pathways were explored, and they all consisted of a common first step involving the formation of a deep potential well. Three favorable pathways were confirmed, and they were the channels producing the adducts CH3CO(NHOH) and CH3NOHCHO and the products H2O and CH3CNO. The Rice-Ramsperger-Kassel -Marcus-canonical variational transition state theory method with Eckart tunneling correction was used to calculate the rate coefficients of the system. The predicted total rate coefficients agree well with the available literature data and show negative temperature dependence and positive pressure dependence. The reaction producing the adduct CH3CHOHNO in the entrance channel is dominant at 1.0 bar, and its branching ratio is almost 100% at a temperature less than 670 K. At 3.0 Torr, it is only dominant at a temperature less than 600 K.Keywords:
Bar (unit)
Atmospheric temperature range
Transition state theory
Reaction rate
Abstract In this work, we have calculated rate constants for the tropospheric reaction between the OH radical and ‐dimethoxyfluoropolyethers. The latter are a specific class of the hydrofluoropolyethers family with the general formula , from which we have selected three case studies: , , and . The calculations were performed by applying a cost‐effective protocol developed for bimolecular hydrogen‐abstraction reactions and based on multiconformer transition state theory relying on computationally accessible M08‐HX/apcseg‐2//M08‐HX/pcseg‐1 calculations. Within the protocol's uncertainties and approximations, the results show that (1) the calculated rate constants have the same order of magnitude and (2) if observed together with previous experimental and theoretical investigations, the chain length (that varies with q and p ) is seen to have a small effect on the rate constant, which is consistent with the “no discernible effect” reported in the experimental work.
Transition state theory
Hydrogen atom abstraction
Constant (computer programming)
Abstraction
Reaction rate
Chain reaction
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The mechanism and kinetics of the H-abstractions of ethylvinylketone (CH2=CHCOCH2CH3) with Cl atom have been carried out using density functional theory (DFT). The electronic structures and frequencies of reaction species are carried out at M06-2X/6-31+G(d,p) level. The energy calculation is performed for optimised species at the same functionality but using a 6-311++G(d,p) basis set. We characterised transition states (TSs) in each H-abstraction channel and explored reaction species along with TS involved in CH2=CHCOCH2CH3+Cl reaction on the potential energy diagram. Among the various H-abstraction channels, H-abstraction from the methylene group (–CH2–) of CH2=CHCOCH2CH3 is found to be a more dominant reaction channel which is further confirmed by thermochemical analysis. The rate constants of all H-abstraction reaction channels and overall rate constant are calculated using canonical transition state theory (TST) within the temperature range of 200–400 K. The value of the overall rate constant at 298.15 K and 1atm pressure is found to be 0.94 × 10−10 cm3 mol−1 s−1, which is in close with the experimental reported rate constant value, i.e. (2.91 ± 1.10) × 10−10 cm3 mol−1 s−1. The percentage branching ratios of each H-abstraction reaction channel, as well as the lifetime of the titled compound, are also reported herein.
Transition state theory
Methylene
Transition state
Reaction rate
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Transition state theory
Substitution (logic)
Substitution reaction
Transition state
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Abstract The reaction rate of the alkaline hydrolysis of ethyl acetate was studied by means of a continuous measurement of the electric conductivity change. The second-order rate constant decreased as the reaction proceeded. The decrease was evident when the initial concentrations of the ester and the base were close together. The initial rate constant at 25°C was measured as 0.1120 1./mol./sec. and the activation energy was 11.56 kcal./mol., values agreed well with those of previous studies. From the standpoint of the electronic theory of organic chemistry, Day and Ingold proposed a sequential reaction mechanism passing through an addition complex. The results of the approximate calculations to the pseudo-first-order reaction and the analog-computation of the exact models coincided with the experimental results. The difference in the activation energies of the forward and reverse reaction rates was calculated from the experimental data. At lower temperatures this reverse reaction rate was small, and the overall reaction rate was approximated as a pure second-order reaction. Other probable reasons for the rate constant decrease were also discussed.
Alkaline hydrolysis
Reaction rate
Rate equation
Reversible reaction
Base (topology)
Constant (computer programming)
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Transition state theory
Kinetic isotope effect
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Long-path FTIR spectroscopy and ab initio calculations combined with conventional transition state theory were used to study the kinetics of the reactions of Cl atoms with deuterated methanes. The following experimental relative rate constants for the reaction of Cl atoms at 298 ± 5 K and 760 ± 5 Torr were determined: CH3D, (6.5 ± 0.5) × 10-14; CH2D2, (4.2 ± 0.5) × 10-14; CHD3, (1.9 ± 0.3) × 10-14; CD4, (5.4 ± 0.4) × 10-15. All experimental and theoretical rate constants are in units of cm3 molecule-1 s-1 and are relative to the 1.0 × 10-13 cm3 molecule-1 s-1 rate constant for the reaction of Cl with CH4. All experimental uncertainty limits are 2σ. The geometries, energies, and frequencies of the reactants, products, and transition states were calculated at the level of the second-order Møller−Plesset approximation using a 6-311++G(2d,2p) basis set. The following theoretical relative rate constants were calculated at 298 K using conventional transition state theory combined with an Eckart one-dimensional tunneling correction: CH3D, 6.8 × 10-14; CH2D2, 4.2 × 10-14; CHD3, 2.1 × 10-14; CD4, 4.4 × 10-15. The theoretical rate constants agree well with the experimental results. The curvature in both the experimental and theoretical rate constants as a function of deuteration is due to a secondary kinetic isotope effect, involving mainly the rate constant preexponential factors. The large decrease in Cl atom rate constant in going from CH4 to CH3D (i.e., the increase in curvature at CH3D) is due to the reduced symmetry in the transition state and a mass-dependent effect. The implications for previous studies, atmospheric chemistry, and chemical reactivity are discussed.
Kinetic isotope effect
Transition state theory
Transition state
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There are different methods to calculate the rate constant of a bimolecular reaction. In this article are described two methods to calculate the rate constant and then these methods are compared using two-channel reaction. The rate constants for each reaction channel are calculated using Transition State Theory (TST) incorporating the Winger tunneling correction and the hindered rotor approximation. Furthermore, the rate constants for the dominant channel are calculated using general equation, which takes into account the rotational energy, is derived from Rice–Ramsperger–Kassel–Marcus (RRKM) theory, using the simplified version of the statistical adiabatic channel model theory. The vibrational mode analysis is used to elucidate the relationships of the reactant region (s = −∞), the saddle point (s = 0) and the product region (s = +∞).
Transition state theory
Saddle point
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From the catalystic dechlorination rates of trichloroethylene with four types of iron particle determined by the static method, it was confirmed that the reaction rates of these particles can be expressed as a pseudo-first-order reaction and that α-Fe · Fe3O4 composite nanoparticles showed the highest reaction rate. As determined by static method, the “specific” reaction rate constants of iron nano- and microparticles tended to remain at certain values. Whereas they tended to decrease when the load of the particles increased. The reaction rate and “specific” reaction rate constants of iron nano- and microparticles decreased when the initial TCE concentration was high increased. The reaction rate constants of iron nanoparticles decreased markedly at a low pH and they increased at a high pH. However, the reaction rate constants of iron microparticles hardly depended on pH.
Reaction rate
Particle (ecology)
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Semiclassical transition state theory, in combination with high accuracy quantum chemistry, is used to compute thermal rate constants from first principles for the O(3P) + H2 reaction and its isotopic counterparts. In the temperature regime of 298–3500 K (which spans 8 orders of magnitude for rate constants), our theoretical results are in excellent agreement (within 5–15%) with all available experimental data from 298 to 2500 K but are somewhat too low (from 15 to 35%) at higher temperatures. Several possible reasons that might cause the degradation at high temperatures are discussed. Vibrational state-selected rate constants and their correlations with normal thermal rate constant are derived and are given in the Supporting Information.
Semiclassical physics
Transition state theory
Kinetic isotope effect
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Hydrogen atom abstraction
Transition state theory
Methyl formate
Transition state
Atmospheric temperature range
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