Substituent and solvent effects on the proton transfer equilibrium in anils and azo derivatives of naphthol.: Multinuclear NMR study and theoretical calculations

The tautomeric equilibrium due to proton transfer is compared in a series of anils of 2-hydroxynaphthalene-1-carbaldehyde and azo derivatives of 2-naphthol. Although structurally similar, these systems suffer different substituent effects on the solution-state proton transfer properties. The comparative study was performed using H-1, C-13 and N-15 NMR spectroscopy in a variety of solvents. Hartree-Fock ab initio calculations involving relative stability of tautomers and full geometry optimization for the ground state are in agreement with the experimental observations. (C) 2003 Elsevier B.V. All rights reserved.