Substituent effects on direct and indirect tautomerism of pyrimidin-2(1H)-one/pyrimidin-2-ol

ABSTRACT

The conversion of pyrimidin-2(1H)-one into pyrimidin-2-ol through direct and indirect mechanisms was investigated in the gas phase and solution media at the B3LYP/6-311++G** level of theory. The kinetic parameters demonstrate that the barrier energy ΔG^≠ of the tautomeric conversion when proton transfer is mediated by one water molecule is almost the same as when is mediated by two water molecules, and is smaller than that when is mediated by three water molecules (14.0 and 17.1 kcal/mol at 298 K, respectively). It is obvious that the indirect mechanism, which is occurred in the presence of solvent molecules, is kinetically favourable in the gas phase and aqueous media. In addition, the decrease in the ΔG^≠ values by the electron donor substituents located at the meta and para positions of pyrimidin-2(1H)-one is larger than those by the electron-withdrawing substituents.

KEYWORDS:

• Pyrimidin-2(1H)-one
• tautomeric conversion
• ab initio
• substituent effects
• solvent effects

ORCID

Leily Heidarpoor Saremi http://orcid.org/0000-0001-5073-4633

Milad Lagzian http://orcid.org/0000-0002-6495-8774