GROUND-STATE LACTIM LACTAM EQUILIBRIUM AND EXCITED-STATE PROTON-TRANSFER OF METHYL 2-HYDROXY-6-METHYLNICOTINATE

The excited-state intramolecular proton-transfer compound methyl 2-hydroxy-6-methylnicotinate (MHMN) has been investigated The ortho position of the hydroxyl group with respect to the pyridine nitrogen for MHMN results in significantly different molecular properties than the molecule that has the hydroxyl group in the meta position. The ground-state lactim-lactam equilibrium constant for MHMN is calculated to be 0.065 ± 0.006 in n-hexane by the absorption measurement. Multiple fluorescences at room temperature were recorded consisting of lactam-form normal emission and lactim-form normal and tautomer emissions. An excited-state intramolecular proton-transfer rate of ≫ 1.0 × 1011 s-1 for the lactim form is deduced from picosecond fluorescence measurements at room temperature. © 1990 American Chemical Society.