Density functional theory was used to study the tautomerization of 4-bromo substituted 1Hpyrazoles
in different solvents. Mechanism and transition state structures of five tautomeric reactions
were detected using quadratic synchronous transit with B3LYP method. The effect of solvent was
considered with PCM method. We have found that the tautomerization is done through the transferring
of hydrogen atoms between two nitrogen atoms in all tautomeric reactions. Also, it was found that the
tautomeric reaction rate is dependent on solvent and reach to constant value for solvents with dielectric constant of greater
than 8.93. Moreover, we found that the effect of solvent on equilibrium constant is dependent on considered molecules.
Keywords: Ab initio, density functional calculations, equilibrium constant, Gibbs free energy, kinetics.
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