Possibility of non-adiabatic level crossing by DFT study of tautomerism and potential
energy surfaces in of 3-hydroxy-5-(pyrimidin- 2-yl)-2H-pyrrol-2-one and its tautomer

J. Phys. Org. Chem. 2011, 24 414–422

Hossein Tavakola* and Hassan Sabzyanb

Abstract
3-Hydroxy-5-(pyrimidin-2-yl)-2H-pyrrol-2-one (HYPO, T1) and 2-hydroxy-5-(pyrimidine-2-yl)-3H-pyrrole-3-one (HYPO, T2) have designed in this research to study potential energy curves for their dynamic motions and possibility of crossing between levels. Study of tautomerism shows that T1 tautomer is more stable than T2 (about 5.83 kJ/mol). Dynamic study of possible motions show rate constants (highest possible) equal to 8.82 M/s for tautomerism, 1.70T109 M/s for relative rotation of ring (rr) and 3.67T106 M/s for rotation of OH bond (br). Moreover, variations of orbital populations, NBO charges, hybridations, and acceptor–donor interactions in IRC steps have been investigated to study the possibility of non-adiabatic crossing between tautomerism and ring rotation potential energy curves. The data showed that in spite of the fact that these two potentials share three common points, these two potential curves cannot have non-adiabatic crossing because of different symmetries and a large difference between their barrier energies.