Spectroscopic and semi-empirical MO study of substituent effects on the intramolecular proton transfer in anils of 2-hydroxybenzaldehydes

Substituent effects in singly and doubly substituted anils of 2-hydroxybenz aldehyde showing strong intramolecular hydrogen bonding are studied on the basis of solution C-13 NMR spectroscopic data and semiempirical MO (AM1) ca lculations of the relative stability of tautomers. Excited state proton tra nsfer is also investigated using electronic absorption and fluorescence spe ctroscopies, and calculation of vertical excitation energies (INDO/S). The theoretical predictions are in agreement with the experimental observations . (C) 1999 Elsevier Science B.V. All rights reserved.