Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment and General Theory 2010-12-09

Tautomerism in 4-hydroxypyrimidine, S-methyl-2-thiouracil, and 2-thiouracil.

Barbara M Giuliano, Vitaliy Feyer, Kevin C Prince, Marcello Coreno, Luca Evangelisti, Sonia Melandri, Walther Caminati

Index: J. Phys. Chem. A 114(48) , 12725-30, (2010)

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Abstract

The keto-enol tautomerism of 4-hydroxypyrimidine and of the related molecules S-methyl-2-thiouracil and 2-thiouracil has been investigated using synchrotron-based techniques. The populations of the constituent tautomers and thermodynamic parameters have been obtained by analysis of core-level photoemission spectra. The effect of substituents on the stability of tautomers has been revealed. Attaching additional OH (or SH) groups to the aromatic ring stabilizes the dioxo (or oxo-thione) forms. However, substitution of hydrogen in position 2 by an S-CH(3) group (that is, in going from 4-hydroxypyrimidine to S-methyl-2-thiouracil) does not significantly affect the tautomeric equilibrium.