Photoelectron spectra of hydroxy- and mercapto-pyridines and models of fixed structure

Photoelectron spectra of the title compounds demonstrate that 3- and 4-hydroxy- and 3- and 4-mercapto-pyridine exist in the vapour phase in the hydroxy- and mercapto-forms with less than 5% of the oxo- or thioxo-tautomers. However, although the hydroxy- and mercapto-tautomers are also predominant for the 2-series, significant quantities of 2-pyridone and pyridine-2-thione exist in equilibrium.