Quinoxaline deuteration

Quinoxalin-2-ones are in tautomeric equilibrium with 2-hydroxy-quinoxalines, but physical measurements indicate that both in solution and in the solid state they exist as cyclic amides rather than as hydroxy compounds. Thus quinoxalin-2-one and its A -methyl derivative show practically identical ultraviolet absorption and are bases of similar strength. In contrast, the ultraviolet spectra of quinoxalin-2-one and its 0-methyl derivative (2-methoxyquinoxaIine) are dissimilar. The methoxy compound is also a significantly stronger base (Table II). Similar relationships also exist between the ultraviolet absorption and ionization properties of 3-methylquinoxalin-2-one and its N- and 0-methyl derivatives. The infrared spectrum of 3- (p-methoxy-benzyl)quinoxalin-2-one (77) in methylene chloride shows bands at 3375 and 1565 cm" which are absent in the spectrum of the deuterated... 

The H(D) atom abstraction rate constants in durene crystals by the impurity molecules quinoline, isoquinoline, quinoxaline, and quinozaline in their excited triplet state were measured by Hoshi et al. [1990] using the phosphorescence method described above. The transfer occurs in the fragment CH N formed by a methyl group of durene and a nitrogen atom of the impurity molecule. In the interval 300-100 K the activation energy drops from 3.5 kcal/mol to 1.6 kcal/mol. Deuteration reduces the... 

N-H stretching. The H NMR spectrum, in deuterated acetone, shows a methylene singlet at 5 4.44 and a broad band at 5 5.3 due to N-H absorption, which disappears on addition of D2O. 3-Aryl-l,2-dihydro-quinoxalines give monoacetyl derivatives on treatment with acetic anhydride and are oxidized to the corresponding quinoxalines with ben-zoquinone, ferric chloride, or m-nitrobenzoic acid. Other 1,2-dihydroquinoxalines have been prepared from o-phenylenediamine as illustrated in Scheme 2. 

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