A series of new azo dyes derived from cyclohexane-
1,3-dione have been synthesized and studied as regards
the existence of prototropic tautomerism both in gas
phase and in solution. The calculated equilibrium
constants predicted by DFT method are in agreement
with the NMR experimental results, predicting the
existence of all newly studied dyes predominantly or
completely in their hydrazone forms. The positions of 1H
signals in NMR spectra compare qualitatively with those
predicted computationally at the GIAO/DFT level of
theory. Different bands observed in electronic absorption
spectra have been assigned to the proper electronic
transitions. The new band displayed by compound 5 in
proton accepting solvents was regarded as a result of
ionization. This characteristic band could be useful if the
compound was used as analytical indicator. Analysis of
electronic absorption spectra confirms the conclusions
drawn from calculations and examination of 1H NMR as well as FT-IR spectra.