Abstract
A systematic investigation of the proton transfer in the keto-amino/enol tautomerization of imidazolone was undertaken. Calculations in aqueous solution were performed using both combined discrete/self-consistent reaction field (SCRF) and SCRF methods. Complexes containing one to three water molecules around the hydrophilic site of imidazolone were used for the combined discrete/SCRF calculations. The DFT results predict that the barrier height for non-water-assisted intramolecular proton transfer is very high (214.8 kJmol−1). Hydrogen bonding between imidazolone and the water molecule(s) will dramatically lower the barrier by a concerted multiple proton transfer mechanism. The proton transfer process through a eight-member ring formed by imidazolone and two water molecules is found to be more efficient and the calculated barrier height is ca. 61 kJmol−1.
Figure DFT calculations in aqueous solution predict the H-bonding between imidazolone(IZ) and the water molecule(s) will dramatically lower the tautomeric barrier by a concerted multiple proton transfer mechanism, in which an eight-member ring structure formed by IZ and 2H2O is found to be more efficient and the barrier is 60.8 kJ mol−1, much less than 214.8 kJ mol−1 in the non-water-assisted mechanism.
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This work was supported by the Science Foundation of Chongqing City, PRC (2002–7473).
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Ren, Y., Li, M. & Wong, NB. Prototropic tautomerism of imidazolone in aqueous solution: a density functional approach using the combined discrete/self-consistent reaction field (SCRF) models. J Mol Model 11, 167–173 (2005). https://doi.org/10.1007/s00894-005-0242-0
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DOI: https://doi.org/10.1007/s00894-005-0242-0