Physical Properties of Quinazolines

The resonance energies of several nitrogen heterocyclic compounds including quinazoline (1) were evaluated from bond energies using calculated heats of formation and bond lengths. The data implied that there is much bond localization in the heterocycles. The resonance energy for quinazoline 

The dipole moment of quinazoline was calculated from variable electronegativity self-consistent field (VESCF) molecular orbital procedures with 

55 D) and CJ (2.40 D) integral prescriptions, which gave better values than previous theoretical methods. The observed dipole moment in benzene was 2.2 D, and the agreement between theory and experiment for other heterocycles that were studied was also within 0.4 D. 

The spectra revealed a sharp first system of bands, which rises in a simple pattern of progressions from 27,587 cm . The second system (first n n) is diffuse.  

The fluorescence and phosphorescence of quinazoline, 6-chloro-4-phenyl-and 6-chloro-l-methyl-4-phenylquinazolin-2(lH)-one were recorded in ethanol containing 1% of concentrated sulfuric acid. The luminescence of these compounds on thin-layer chromatography (TLC) plates saturated with ethanol was reported. 4-Morpholino- and 4-piperidino-6-methoxy-2-phenyl-quinazoline also have luminescent properties, and the ultraviolet fluorescence in the crystals and in hexane or benzene solution was discussed. The time and wavelength resolved emission from quinazoline vapor at low pressures was studied with a pulsed frequency double-dye laser and were compared with those of quinoxaline and cinnoline.  

Armarego, in Fused Pyrimidines. Part 1—Quinazolines (D. J. Brown, ed.), Wiley (Interscience), New York, 1967. 

Armarego, in MTP International Review of Science. Organic Chemistry Series One. Heterocyclic Compounds (K. Schofield, ed.), Vol. 4, pp. 153-156. Butterworth, London, 1973. 

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The physical properties of the pyridopyrimidines closely resemble those of their nearest A-heteroeyclie neighbors the quinazolines and the pteridines. Thus, in common with the pteridines, the presence of groups capable of hydrogen-bonding markedly raises the melting point and lowers the solubility. - The acid dissociation constants (pif a values) and ultraviolet absorption spectra of all four parent pyridopyrimidines have been determined by Armarego in a comprehensive study of covalent hydration in these heterocyclic systems. The importance of these techniques in the study of covalent hydration, and... 

In many cases, addition or removal of water proceeds sufficiently slowly that some of the physical properties of unstable species (such as hydrated neutral quinazoline or anhydrous 2-hydroxypteridine) can be observed. In these cases, reaction kinetics can also be examined. Addition of water to pteridine is of special interest in relation to studies of the formation and hydrolysis of Schiflf bases. The reaction proceeds in two reversible stages, 3 4 5 ... 

The present review covers the literature to the end of 1967 and all original sources have been consulted. Syntheses of each of the four ring systems are summarized separately, but physical, chemical, and biological properties are considered generally. Many pjTidopyri-midines were initially synthesized for a study of biological activity or physical properties because of the close structural relationship of these systems to the quinazolines (5) and pteridines (6). Recent reviews have discussed these related compounds. 

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