DFT and MP2 study of simple and water-assisted tautomerism in amidrazones |
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Authors: | Tavakol Hossein |
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Institution: | (1) Department of Chemistry, Faculty of Science, University of Zabol, Zabol, Iran |
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Abstract: | DFT and MP2 methods were used to calculate structural parameters, vibrational modes, solvent effect, and energetic properties
of amidrazones. Amidrazones can be presented by three tautomeric forms and six isomers. All tautomers and transition states
were optimized at the B3LYP/6-311++g** and MP2/6-311++G** levels of theory. The relative stabilities of amidrazone isomers
in the gas phase were found to be as 1Z > 1E > 2E > 2Z > 3E > 3Z > TS(1–2) > TS(1–3). The calculated energy differences between E and Z isomers are very low and between different tautomers are nearly low, but the energy barriers for tautomerism interconversions
at the gas phase are high. The kinetic and thermodynamic data in solvents (chloroform, tetrahydrofuran, acetone, and water)
are nearly similar to those in the gas phase but their rate constants are slightly less than those in the gas phase. Moreover,
equilibrium and rate constants of intermolecular tautomerism in presence of 1–3 molecules of water were calculated. Computed
energy barriers show that the barrier energy of water-assisted tautomerism is very lower than that in simple tautomerism and
also calculated binding energies show that water can stabilize transition states more than tautomers. Therefore, this water-assisted
tautomerism can be performed fast, especially with the assistance of two molecules of water. |
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