Kinetics of Hydrogen Abstraction Reaction Class H + H−C(sp³):  First-Principles Predictions Using the Reaction Class Transition State Theory

Abstract

We present an application of the reaction class transition state theory (RC-TST) in predicting thermal rate constants of the hydrogen abstraction reactions H + H-C(sp 3 ) where C(sp 3 ) is a saturated carbon atom. Combining the RC-TST with the linear energy relationship (LER) allows rate constants of any reaction in the class to be estimated from only reaction energy information. We have derived from first-principles all parameters for the RC-TST/LER method so rate constants for any reaction in this class can be predicted from only reaction energy, that can easily be computed from either the density functional theory or semiempirical molecular orbital theory. We have performed error analyses for a large number of reactions in the above class for which some experimental measurements or estimates are available. By comparisons with results from full TST/Eckart calculations we also found the RC-TST/LER method is quite cost-effective and has accuracy comparable to first-principles predictions using more rigorous methodologies.

Hydrogen Radical Additions to Unsaturated Hydrocarbons and the Reverse β‐Scission Reactions: Modeling of Activation Energies and Pre‐Exponential Factors

“…An alternative correlation expressing the tunneling coefficient as function of the reference reaction"s tunneling coefficient, in line with the approach of Truong et al for hydrogen abstractions as discussed in the methodology section, [26,60,66,67] is given in Supporting Information.…”

“…These methods range from correlating the activation energy to the reaction enthalpy, such as Evans-Polanyi correlations and its variations, [15][16][17] Sabbe et al ChemPhysChem 11:195-210 (2010) -pre-reviewed version 2 additivity. [18,19] Among these are: 1. the structural group contribution method of Willems and Froment, [20,21] in which correction terms on the Arrhenius parameters of a reference reaction account for structural differences between the latter and the considered reaction; 2. methods that calculate the thermochemistry of the transition state, such as the method described by Sumathi et al, [22][23][24] 3. the Reaction Class Transition State Theory developed by Truong et al [25,26] and 4. the group additive (GA) method for activation energies as described by Saeys et al [27,28] Experimental determination of all the kinetic and thermodynamic parameters required for these methods is not possible due to scarcity of experimental data. Moreover, experimental determination of rate constants often involves assuming a reaction scheme which can induce a rather large scatter on the resulting reported kinetic data for a given reaction.…”

“…Quantum chemical calculations can be applied to any reaction type, and extracting quantitative values of rate coefficients does not rely on assuming a reaction scheme. Therefore, the use of quantum chemistry to calculate rate coefficients for gas phase radical reactions is particularly attractive and the more recently developed parameterization schemes for carbon centered radical additions and β scissions [29] and for hydrogen abstraction [22][23][24][25][26] are all based on first principles calculations to determine the model parameters.Although hydrogen additions are less commonly studied than hydrogen abstractions or non-hydrogen radical addition, rate coefficients for this reaction family are included in many literature reviews on radical reaction rate coefficients. In general, these reviews report not only experimental data but also predicted and extrapolated data.…”

“…It should be mentioned that correction for tunneling contributions is important at temperatures up to 400 K only. For temperatures of 500 K and higher, tunneling has only a marginal contribution and can thus be neglected.An alternative correlation expressing the tunneling coefficient as function of the reference reaction"s tunneling coefficient, in line with the approach of Truong et al for hydrogen abstractions as discussed in the methodology section, [26,60,66,67] is given in Supporting Information. …”

Application of Chemical Graph Theory for Automated Mechanism Generation

“…In fact, all the parameters needed to determine rate constant can be easily computed or estimated for each species. Currently, this theory is developed for only one reaction class (H abstraction), 33 but work is in progress on other classes. Moreover, the kinetic database populated with experimental and theoretically calculated rate constants is also under development.…”