A Study of Azo-Hydrazone Tautomerism in 3-Phenyl-4-arylazo-5-isozaolones by $^H-NMR$ spectra of $^{15}N-labeled$ Compounds and HMO Method

The tautomerism in 3-phenyl-4-arylazo-5-isoxazolones 1 was examined by $^1H-NMR$ spectra of $^15N-labeled$ compound and by HMO method. Both spectra data $(^1H-NMR\;and\;IR)$ and bonding energies are in support of the assignment of the hydrazone structure to such compounds. It is further shown that intermolecular and intramolecular hydrogen bondings favor the hydrazone tautomer.