Tautomerism in aromatic hydroxy N-heterocyclics in the gas phase by metastable ion mass spectrometry

Abstract

The kinetic energy release associated with the decomposition of metastable ions has been used to differentiate between the hydroxyquinolines and hydroxypyridines and the corresponding tautomeric quinolinones and pyridinones in the gas phase. It is shown that 2-hydroxyquinoline exists in both tautomeric forms, whereas the other monohydroxyquinolines exist only in the hydroxy forms. The hydroxy forms are also favoured for the hydroxypyridines, but both the 3- and 4-isomers show some tendency to occur as the pyridinones, or, for the 3-isomer, the betaine.