Tautomeric azines. Part 6. Phthalazin-1 (2H)-one

Abstract

Phthalazin-1 (2H)-one, its three monomethyl derivatives, and two of its dimethyl monocationic derivatives have been investigated by examining the spectra of the various charged forms and by basicity studies. The tautomeric equilibrium of the parent compound has been elucidated quantitatively, and the minor contributions of lactim and zwitterionic forms have been found. The tautomeric monocations show appreciable contributions from hydroxyforms, which can predominate in high polarity media.