Nuclear Magnetic Resonance Investigations of the Azo–Hydrazone Tautomerism of Azoreactive Dye Chromophores

High-field 1H and 13C NMR methods (e.g. 1H{1H} and 13C{1H} NOE spectroscopy) were used to examine the tautomeric characteristics, particularly with regard to the question of azo–hydrazone tautomerism, of two azo dyes. Full 1H and 13C NMR signal assignments are given for both molecules. The NMR results indicate that in DMSO solution the tautomeric equilibria are shifted predominantly toward the hydrazone from II in both compounds. The presence of a fast II=III interconversion could also be plausibly assumed. © 1997 by John Wiley & Sons, Ltd.