C-13 NMR SPECTROSCOPIC AND AM1 STUDY OF THE INTRAMOLECULAR PROTON-TRANSFER IN ANILS OF SALICYLALDEHYDE AND 2-HYDROXYNAPHTHALENE-1-CARBALDEHYDE

Tautomeric equilibria in intramolecularly hydrogen bonded Schiff bases is studied on the basis of solution C-13 NMR chemical shifts. Variabl e temperature NMR spectroscopic data and comparison with appropriate m odels show that while anils of salicaldehyde exist as phenolic tautome rs, those of 2-hydroxynaphthalene-1-carbaldehyde exist as equilibrium mixtures containing appreciable amounts of both enol and keto tautomer s, the latter being slightly predominant. AM1 results concerning the r elative stability of tautomers are in good agreement with the NMR spec troscopic information.