Tautomerism in side-chain derivatives of n-heterocycles NMR and UV spectra—I

NMR and UV spectra of some (ψ)cyano-, carbethoxy-, and acylmethyl derivatives of 2-oxo-1,2-dihydroquinoxaline, 2-oxo-1,2-dihydro-6,7-benzoquinoxaline, 3,4-dihydro-1,4,2H-benzoxazone, quinaxoline, and quinoline, were recorded in chloroform, dimethyl sulfoxide, and trifluoro- acetic acid. The results indicate the existence of tautomeric equilibria, with noticeable contribution of the enaminic structures B or D, depending on the solvent and the nature of the heterocycle. Relationhips between some NMR parameters and tautomeric structures were observed.