UV-vis and IR spectroscopic studies of some 4-arylhydrazo-2-phenyl-2-oxazoline-5-one derivatives

The absorption spectra of some 4-arylhydrazo-2-phenyl-2-oxazoline-5-one derivatives, have been studied in organic solvents of different polarity. The diagnostic IR spectral bands are assigned and discussed in relation to molecular structure and hydrogen bond existing in the stable compounds in the hydrazo form. The presence of electron withdrawing group in the phenyl ring facilitates the charge migration and hence the proton transfer, thus the azohydrazo form may appear in these compounds, but the major compounds were in the hydrazo form. The fact that these compounds show evidence for intramolecular hydrogen bonding is in favor of the hydrazone structure, this fact excludes the possibility of azo structure. The electronic absorption bands are assigned to the corresponding electronic transitions and the effect of solvent parameters on the charge transfer energy [ECT] is investigated. Four absorbance bands appeared for hydrazones in the range 443-221 nm, the first band has Amax within the range 222-237 nm corresponding to the medium energy transition of the phenyl group e [1]La-[1]A]. The second band with [lambda]max at 243-257 nm is attributed to the low energy mm transition of the phenyl rings representing the [[1]Lb-[1]A] electronic state. The third band at 278-314 nm lies within the energy region for the mm excitation of the electrons of the hydrazo groups. The last band in the visible which has [lambda]max within the range 422-443 nm is considered as being due to an intramolecular charge transfer involving the whole molecule. Finally, the substitution effect was also studied