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Tautomerization reactions of thiobarbituric acid: A detailed kinetic study using combined TST and QTAIM approach
  • Leila Fatahiyan,
  • Afshin Taghva Manesh,
  • Nasrin Masnabadi
Leila Fatahiyan
Islamic Azad University Central Tehran Branch

Corresponding Author:[email protected]

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Afshin Taghva Manesh
Islamic Azad University Central Tehran Branch
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Nasrin Masnabadi
Roudehen Islamic Azad University
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Abstract

The kinetics of tautomerization reactions of thiobarbituric acid were thoroughly investigated at the B3LYP/6-311+G(3df,2p) level of theory and elevated temperatures from 270 K up to 1000 K. The kinetic parameters were determined by employing canonical transition state theory (TST). The quantum tunneling effect was included by both wigner and centrifugal-dominant small-curvature semiclassical adiabatic ground-state approximation methods. Intrinsic reaction coordinate (IRC) analysis was performed to certify a unique connection from an obtained transition state configuration to optimized structures of reactant and product. The reaction forces and reaction force constants were computed across the IRC of each reaction. Then, using extremums of reaction forces, each reaction was partitioned into three stages containing reactant, transition state, and product stages. The extent of reactions was followed along with three reaction stages. The dependence of kinetic parameters and curvature of Arrhenius plots on temperature were investigated and discussed in the framework of TST. To further unveil the mechanism of the reactions, the quantum theory of atoms in molecules (QTAIM) was applied. To do this aim, QTAIM descriptors on the BCP of involved bonds including the density of electrons, Laplacian of the density of electrons, Lagrangian kinetic energy, potential energy, and energy density were computed and surveyed along with reaction extent through IRC.