Quinazoline infrared spectra

The hydrochloride of (3) holds water rather tenaciously, and the infrared spectrum indicates that the water is covalently bound. Mild oxidation of the cation (3) gives 4-hydroxyquinazoline in high yield and ring-chain tautomerism is excluded on the grounds that quinazo-line does not give a positive aldehyde test in acid solution, 2-Methyl-quinazoline also has an anomalous cationic spectrum and a high basic strength (see Table I), but 2,4-dimethylquinazoline is normal in both these respects, which supports the view that abnormal cation formation entails attack on an unsubstituted 4-position. ... 

Quinazoline-2,4-dione (108) has been assigned the dioxo formulation on the basis of its infrared spectrum. A dioxo structure has also been demonstrated for the derivative 108a by ultraviolet spectral comparisons and infrared data. ... 

The infrared spectrum of quinazoline and other diazanaphthalenes were measured, and the vibrational fundamentals were assigned from Raman polarization data. The Raman spectrum of quinazoline in aqueous solution has fourteen bands that appear to be polarized. All the band frequencies, except for those at 1330 and 1334 cm were consistent with the frequencies assigned as fundamentals in the spectrum of naphthalene. The infrared spectra of several quinazolin-4(3H)-ones and their 3-acetyl, 3-acetoxy, and 3-hydroxy derivatives were examined at wave numbers lower than 3000 cm Bands due to NH stretching vibrations provided evidence for cyclic dimeric association between molecules. The zwitterionic structure (3) was proposed for 3-hydroxyquinazolin-4-one. ... 

Anhydrous quinazoline hydrochloride absorbs one molecule of water readily, and. the product is difficult to dehydrate completely even in a high vacuum at 60°. Infrared spectral data suggest that this water is covalently bound because of (o) the absence of several bands in the spectrum of the hydrate which are present in the spectrum of the anhydrous hydrochloride and (6) the presence of extra bands at 1474 and 1240 cm that have been attributed to C— H and O— H bending vibrations of the — CHOH group. 

The anomalous behavior of quinazoline was first discovered by Albert et who made the surprising observation that 4-methyl-quinazoline 2.5) was a weaker base than quinazoline (pA 3.5). Mason then observed that the ultraviolet spectrum of the quinazoline cation was abnormal but that the spectrum of 4-methylquin-azoline was normal (see Fig. 2). These anomalies led to the suggestion that water adds covalently to the cation of quinazoline to give 12 (R = H). The occurrence and position of hydration were confirmed by a detailed study of the ultraviolet and infrared spectra of the anhydrous and hydrated hydrochlorides and by mild oxidation of the cation to 4(3 )-quinazolinone. Using the rapid-reaction technique (the continuous-flow method), the spectrum of the unstable... 

Two new quinazoline alkaloids of unusual structure were obtained from the seed husks of Zanthoxylum arborescens.12 Infrared, H n.m.r., and mass spectroscopy showed that the major alkaloid was a quinazolone containing a phenethyl substituent. The 13C n.m.r. spectrum indicated that an iV-methyl rather than an O- methyl group was present, but the spectroscopic studies did not distinguish between structures (19 R = H) and (20 R = H). The alkaloid was shown to be the iV-phenethyl derivative (20 R = H) by synthesis (Scheme 4), and a minor... 

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