Kinetics of 1,4-Hydrogen Migration in the Alkyl Radical Reaction Class

Abstract

The kinetics of the 1,4-intramolecular hydrogen migration in the alkyl radicals reaction class has been studied using reaction class transition-state theory combined with the linear energy relationship (LER) and barrier height grouping (BHG) approach. The rate constants for the reference reaction of n-C(4)H(9) were obtained by canonical variational transition-state theory (CVT) with the small curvature tunnelling (SCT) correction in the temperature range 300-3000 K with potential-energy surface information computed at the CCSD(T)/cc-pVDZ//BH&HLYP/cc-pVDZ level of theory. Error analyses indicate that RC-TST/LER, where only reaction energy is needed, and RC-TST/BHG, where no other information is needed, can predict rate constants for any reaction in this reaction class with excellent accuracy. Specifically, for this reaction class the RC-TST/LER method has less than 65% systematic errors in the predicted rate constants, while the RC-TST/BHG method has less than 80% error when compared to explicit rate calculations.

Kinetics of the hydrogen abstraction ·C2H5 + alkane → C2H6 + alkyl reaction class: an application of the reaction class transition state theory

“…Previous applications of RC-TST, hybrid non-local density functional theory (DFT), particularly Becke's half-and-half (BH&H) non-local exchange, and Lee-Yang-Parr (LYP) non-local correlation functional, have been found to be sufficiently accurate for predicting the transition state properties for different classes of reactions [24,[27][28][29]. Recently, there have been a number of new DFT functional developments, such as the non-local M062X functional [33], designed especially for the chemical kinetics purposes.…”

“…In our previous studies [23,26,27], we suggested the use of the smallest reaction, that is, the principal reaction (PR) of the class, to be the reference reaction since its rate constants can be calculated accurately from first principles or are often known experimentally. However, we found that the principal reaction is not always the best reference reaction, and it is also true here.…”

“…The assumption is that these correlation expressions can be extended to all reactions in the class. So far, this assumption has been shown to be valid for different reaction families [10,[23][24][25][26][27][28][29].…”

Kinetics of the hydrogen abstraction ROH + H → RO• + H2 reaction class

“…Such generic rate rules have significant advantages over relying on a library of individual reaction rate constants and their associated T dependency [13]. The group additivity for transition states [14][15][16] (GA) and reaction class transition state Theory [17][18][19][20][21][22][23] (RC-TST) were demonstrated to be powerful methods for filling the gap. By generalizing from smallmolecule reactions to larger homologues, these methods provide an effective way to extrapolate accurate rate constants from a small number of reactions to the whole reaction class.…”

“…The assumption is that these correlation expressions can be extended to all reactions in the class. So far, this assumption has shown to be valid [17,[19][20][21]23]. To develop RC-TST/LER (linear energy relationship) parameters for the title reaction class, the representative set consists of 19 reactions as shown below:…”