Development of Predictive Models of the Kinetics of a Hydrogen Abstraction Reaction Combining Quantum-Mechanical Calculations and Experimental Data

Abstract

The importance of developing accurate modelling tools for the prediction of reaction kinetics is well recognised. In this work, a thorough investigation of the suitability of quantum mechanical (QM) calculations to predict the effect of temperature on the rate * To whom correspondence should be addressed provide good correlated rate-constant values and to be competitive with conventional kinetic models, i.e., the Arrhenius and the three-parameter Arrhenius models. This combination of QM-calculated and experimental data sources is proved particularly beneficial when fitting to scarce experimental data. In this case, the model built on the hybrid strategy has parameters with significantly reduced uncertainty (reflected in the much narrower 95% confidence intervals) compared with the conventional kinetic models while also capturing well the experimental reaction rates with a MAE ln of the rate constant of 0.118. This provides a useful strategy for kinetic model development.

Theoretical Studies of the Hydrogen Abstraction from Poly(oxymethylene) Dimethyl Ethers by O2 in Relation with Cetane Number Data

“…The rate constant is calculated at 1000 K, which is used to simulate the temperature in the combustion chamber of the diesel engine. Consequently, the rate constant for these initiation steps k i ,TST is computed using conventional TST 4,6,26 in the followingwhere κ is the transmission coefficient of the corrected tunneling effect, k B is the Boltzmann constant, h is the Planck constants, R is the gas constant, and Δ G i , T 0 is the standard state Gibbs free energy of activation at temperature T and pressure P 0 = 1 atm. In this work, Δ G i , T 0 has been replaced by Δ E in the calculation process of k i ,TST .…”

“…In this work, Δ G i , T 0 has been replaced by Δ E in the calculation process of k i ,TST . Tunneling effects may be described quantitatively as the Wigner correction factor 26,27 where v ⧧ (cm –1 ) is the magnitude of the imaginary frequency of the TST. However, the tunneling effect has little effect at high temperature, such as 1000 K. Furthermore, the imaginary frequencies of all reactions studied here are exactly similar, and the correction of the tunneling effect has no significant effect on the observed relative reactivity.…”

Collision-Energy Dependence of the Uptake of Hydroxyl Radicals at Atmospherically Relevant Liquid Surfaces

“…E a has been extensively measured for ethane, , with broad agreement that the experimental value at temperatures in the vicinity of 300 K is around 8.9 kJ mol –1 . Sophisticated transition-state theory calculations, which incorporate the other temperature-dependent factors responsible for the curvature in Arrhenius plots, have shown that the experimental rate constants can be reproduced faithfully over the full measured range (200–1250 K) based on a zero-point-energy-corrected barrier height of 6.7 kJ mol –1 . In the absence of equivalent detailed information, we make the assumption that a similar ratio between empirical, room-temperature E a and threshold energies E 0 also applies to larger alkanes.…”

“… a Based on neopentane. b Based on cyclohexane. c Based on an average of 2,3-dimethylbutane and 2,3,4-trimethylpentane. d From ref . e From ref . f As estimated here by analogy with ethane, as described in the text. …”

“…Sophisticated transition-state theory calculations, which incorporate the other temperature-dependent factors responsible for the curvature in Arrhenius plots, have shown that the experimental rate constants can be reproduced faithfully over the full measured range (200−1250 K) based on a zero-pointenergy-corrected barrier height of 6.7 kJ mol −1 . 89 In the absence of equivalent detailed information, we make the assumption that a similar ratio between empirical, roomtemperature E a and threshold energies E 0 also applies to larger alkanes. Site-specific E a values are available for a range of alkanes; we have selected the largest molecules for which data are available in which the abstraction takes place either exclusively or predominantly around room temperature from a single C−H bond type.…”