Ab initio group contribution method for activation energies for radical additions

Kinetics of α hydrogen abstractions from thiols, sulfides and thiocarbonyl compounds

“…[22][23][24][25][26][27][28][29][30][31][32][33] Sumathi et al 27,28 proposed a method to obtain accurate kinetic data for hydrogen abstraction reactions using supergroups that encompass the reactive moiety of the transition state structure. The major advantage of these supergroups is that they can account for non-atom-centered contributions, i.e.…”

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

“…Possible steric interactions that cannot be accounted for in the group additive method are considered as tertiary contributions. Saeys et al [27] showed that secondary and tertiary contributions can usually be neglected for carboncentered radical additions. Due to the small dimensions of the adding hydrogen radical, the error introduced by neglecting secondary and tertiary contributions can be expected to be even smaller for hydrogen than for carbon-centered radical additions.…”

“…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.…”

“…[29] The computational approach involves conventional transition state theory based on high-level CBS-QB3 ab initio calculations, [52] which has already shown its accuracy for similar radical reactions in previous work. [27][28][29]53] In this paper, first the computational method is validated for hydrogen additions by comparing the CBS-QB3 rate coefficients with computational experimental data available in literature. Next, rate coefficients are calculated for 34 reactions, from which 33 group additive values are derived, and a model to correct for tunneling effects is proposed for rate predictions at temperatures below 1000K.…”

“…Moreover, both methods are limited to predictions of the activation energy and do not allow prediction of the pre-exponential factor. To the best of our knowledge, no structure-reactivity correlation covering a wide range of hydrogen additions to hydrocarbons is available in literature.This work aims at the determination of a consistent set of group additive values (∆GAV°) for the prediction of activation energies and pre-exponential factors of hydrogen additions to a broad range of hydrocarbons and the reverse C−H β scissions, in line with the recently reported group additive model for carboncentered radical addition.[29] The computational approach involves conventional transition state theory based on high-level CBS-QB3 ab initio calculations, [52] which has already shown its accuracy for similar radical reactions in previous work.[ [27][28][29]53] …”