Synthesis, characterization and intramolecular proton transfer of 3,3′-dihydroxy-4,4′-[5-methyl-1,3-phenylenebis(nitrilomethylidyne)]-bis-phenol.

Highlights: [•] A new ONNO tetradentate Schiff base has been synthesized and characterized experimentally and theoretically, too. [•] Geometries of its tautomers were optimized. [•] Theoretical assignments of the IR and NMR spectra have been computed. [•] Its tautomerism was demonstrated by kinetical and AIM analysis. [ABSTRACT FROM AUTHOR]