# Interpretation and Application of Reaction Class Transition State Theory for Accurate Calculation of Thermokinetic Parameters Using Isodesmic Reaction Method

journal contribution

posted on 19.02.2016, 10:50 by Bi-Yao Wang, Ze-Rong Li, Ning-Xin Tan, Qian Yao, Xiang-Yuan LiWe
present a further interpretation of reaction class transition
state theory (RC-TST) proposed by Truong et al. for the accurate calculation
of rate coefficients for reactions in a class. It is found that the
RC-TST can be interpreted through the isodesmic reaction method, which
is usually used to calculate reaction enthalpy or enthalpy of formation
for a species, and the theory can also be used for the calculation
of the reaction barriers and reaction enthalpies for reactions in
a class. A correction scheme based on this theory is proposed for
the calculation of the reaction barriers and reaction enthalpies for
reactions in a class. To validate the scheme, 16 combinations of various
ab initio levels with various basis sets are used as the approximate
methods and CCSD(T)/CBS method is used as the benchmarking method
in this study to calculate the reaction energies and energy barriers
for a representative set of five reactions from the reaction class:
R

_{c}CH(R_{b})CR_{a}CH_{2}+ OH^{•}→ R_{c}C^{•}(R_{b})CR_{a}CH_{2}+ H_{2}O (R_{a}, R_{b}, and R_{c}in the reaction formula represent the alkyl or hydrogen). Then the results of the approximate methods are corrected by the theory. The maximum values of the average deviations of the energy barrier and the reaction enthalpy are 99.97 kJ/mol and 70.35 kJ/mol, respectively, before correction and are reduced to 4.02 kJ/mol and 8.19 kJ/mol, respectively, after correction, indicating that after correction the results are not sensitive to the level of the ab initio method and the size of the basis set, as they are in the case before correction. Therefore, reaction energies and energy barriers for reactions in a class can be calculated accurately at a relatively low level of ab initio method using our scheme. It is also shown that the rate coefficients for the five representative reactions calculated at the BHandHLYP/6-31G(d,p) level of theory via our scheme are very close to the values calculated at CCSD(T)/CBS level. Finally, reaction barriers and reaction enthalpies and rate coefficients of all the target reactions calculated at the BHandHLYP/6-31G(d,p) level of theory via the same scheme are provided.