A MULTINUCLEAR NMR-STUDY OF PROTON-TRANSFER PROCESSES IN SCHIFF-BASES

H-1, C-13 and N-15 NMR data are reported for seven Schiff bases in ord er to study the possibility of proton transfer from oxygen to nitrogen . The compounds contain various substituents which influence the acidi ty of the OH group and the basicity of the nitrogen atom. All the NMR results provide a consistent view of the extent of proton transfer. Th e reported value of (1)J(N-15-H-1) is used to give a quantitative esti mate of this extent, Low temperature N-15 NMR results for compound 7 s how an increase in proton transfer with respect to that found for this molecule at room temperature.