Original Articles: 2013 Vol: 5 Issue: 6
Equilibrium, kinetic and thermodynamic studies of silarhodanine tautomers by highly CBS-Q method
The proton transfer processes have generated eight minimum structures of the silarhodanine molecule. These structures were studied in the gas phase by a high level theory complete basis set (CBS-Q). All the structure are heterocyclic compounds except S2 structure. The global isomeric structure was S5 at the CBS-Q levels of theory. The acyclic structure S2 is possessed the highest energy (60.17 kcal/mol) above the global minimum S5. Nine anions and nine cations of various conformers have been investigated. The protonation and deprotonation reactions in the gas phase are examined at the CBS-Q level. The S2OA showed the highest relative enthalpy (ΔH= 24.65 kcal/mol) and S3OA structure showed the highest Gibbs free energy (ΔG=23.59 kcal/mol). The S2NC cation showed the highest relative enthalpy and Gibbs free energy (ΔH= 50.25 kcal/mol, ΔG=47.07 kcal/mol) in the cations section. Energetically easiest process is the deprotonation of 2ZNA with the computed enthalpy and Gibbs free energy of 1274.52 kJ/mol and 1282.49 kJ/mol. The equilibrium constants at 298.15 K and 1 atmosphere pressure of the deprotonation reactions are very small which means the reaction at this temperature favor the reactants. The computed vibrational frequencies values for the structures are inconformity with the experimental ones.