Ultraviolet spectra, hydrogenation

P-Hydroxy-A-norpregn-3(5)-en-2-one (7) A solution of the hydroxy-methylene steroid (5) (24.8 g) dissolved in 240 ml of acetic acid and 240 ml of ethyl acetate is ozonized at — 10° with one molar equivalent of ozone. The resulting solution is diluted with 240 ml. of water and 60 ml of 30 % hydrogen peroxide and allowed to stand overnight. The solution is diluted with 1.5 liters of water and extracted with 3 x 700 ml portions of ethyl acetate. The combined extracts are washed with water, saturated sodium chloride solution, dried over sodium sulfate and concentrated to dryness under vacuum, leaving 23.4 g of a colorless amorphous residue of crude diacid. This material shows a maximum in the ultraviolet spectrum at 224 mp (s 6,400) indicating a 53 % yield of unsaturated acid (6). It is used without further purification. 

The electronic spectrum of a compound arises from its 7r-electron system which, to a first approximation, is unaffected by substitution of an alkyl group for a hydrogen atom. Thus, comparison of the ultraviolet spectrum of a potentially tautomeric compound with the spectra of both alkylated forms often indicates which tautomer predominates. For example, Fig. 1 shows that 4-mercaptopyridine exists predominantly as pyrid-4-thione. In favorable cases, i.e., when the spectra of the two alkylated forms are very different and/or there are appreciable amounts of both forms present at equilibrium, the tautomeric constant can be evaluated. By using this method, it was shown, for example, that 6-hydroxyquinoline exists essentially as such in ethanol but that it is in equilibrium with about 1% of the zwitterion form in aqueous solution (Fig. 2). 

In 1882 Baeyer and Oekonomides advanced formula 72 (R = H) for isatin on chemical grounds, but shortly thereafter the dioxo structure 73 (R H) was proposed since the ultraviolet spectrum of isatin resembled that of the N—Me derivative (73, R Me) and not that of the O—Me derivative (72, R = Me). " It was later shown, despite a conflicting report, that the ultraviolet spectrum of isatin is very similar to the spectra of both the O— and N—Me deriva-tives - the early investigators had failed to take into consideration the facile decomposition of the O—Me derivative. Although isolation of the separate tautomers of isatin has been reported, - these claims were disproved. A first attempt to determine the position of the mobile hydrogen atom using X-ray crystallographic techniques was inconclusive, but later X-ray work," dipole moment data, and especially the infrared spectrum demonstrated the correctness of the... 

Lyman band spect A band in the ultraviolet spectrum of molecular hydrogen, extending from 125 to 161 nanometers. iT-mon. band ... 

Lyman series spect A group of lines in the ultraviolet spectrum of hydrogen covering the wavelengths of 121.5-91.2 nanometers. iT-mon, sir-ez lyonium ion chem The cation that is produced when a solvent molecule is protonated. iT an-e-om, T-3n ... 

In the latter case the structure was established by reduction with stannous chloride in acetic acid, which afforded the imidazole derivative (104), thus proving ortho substitution, followed by comparison of the ultraviolet spectrum of 104 with the two possible benzimidazole derivatives of carbazole. Deamination of 103 via diazotization in sulfuric acid afforded 1-nitrodibenzothiophene (105) (54%), being the only recorded route to this compound (Scheme 5). Initial attempts to hydrolyze 102 to the nitroamine (103) had been made with ethanolic hydrogen chloride... 

Subsequent to the discovery of the Balmer series of lines in the visible region of the electromagnetic spectrum, it was found that many other spectral lines are also present in nonvisible regions of the electromagnetic spectrum. Hydrogen, for example, shows a series of spectral lines called the Lyman series in the ultraviolet region and still other series (the Paschen, Brackett, and Pfund series) in the infrared region. 

A third dimer was obtained from Norway sprucewood in somewhat impure condition (m.p., 117°-127°C.). However, its vapor phase retention time and ultraviolet spectrum 23) were identical with those of authentic 5,5 -diethyl-2,2 -dihydroxy-3,3 -dimethoxybiphenyl (VII), m.p. = 143°C. (P). Furthermore, the NMR spectrum and melting point of its purified diacetate were identical with those of the synthetic compound. The corresponding 5,5 -di-w-propyl derivative has already been isolated from neutral hydrogenation of softwood lignin in our laboratory 18). 

In a study of the lithium aluminum hydride reduction of a series of nitrogen aromatic heterocyclics, Bohlmann97 found that this metal hydride effected a conversion of acridine to 9,1O-dihydroacridine (91) in high yield and purity. The ultraviolet spectrum of the isolated dihydroacridine (Amax 288 mp, loge = 4.18) was confirmed by Braude et al.92 as a part of a study of the hydride donor properties of a series of aromatic nitrogen-heterocycles. These workers found that the dihydroacridine underwent a slow oxidation to acridine in air and a rapid hydrogen transfer in the presence of chloranil to form the quinol and acridine. The dihydroacridine was, however, quite stable under dry nitrogen. 

Physical Chemical Characterization. Thiamine its derivatives, and its degradation products have been fuUy characterized by spectroscopic methods (9,10). The ultraviolet spectrum of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole jlid (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the pTC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the parent cation and its major fragmentation ion, the pyrimidinylmetbyl cation (16). 

Quinoxalin-2-ones show carbonyl stretching absorption in the region of 1660-1690 cm both in Nujol mulls and KBr discs. The ultraviolet spectrum of quinoxalin-2-one shows maxima at 343,287,254,250, and 228 nm in aqueous solution at pH 4.0 and is closely similar to that of its 1-methyl derivative. These data indicate that quinoxalin-2-one exist predominately in the cyclic amide form rather than as 2-hydroxyquinoxaline, and this conclusion is further supported by the closely similar pX values of quinoxalin-2-one and its 1-methyl derivative, which are -1.38 and -1.15, respectively. 2-Methoxyquinoxaline is by comparison an appreciably stronger base, with a pKa value of 0.28. ° X-Ray examination of crystals of quinoxalin-2-one confirms that it exists in the cyclic amide form. °° Quinoxalin-2-one fragments in the mass spectrometer, as might be expected, by the successive loss of carbon monoxide and hydrogen cyanide from the molecular ion. ... 

This ring system has also been called pyrazolo[2,3-a]quinoxaline and pyrazolo[a]quinoxaline. Little work has however been done on this heterocycle. Catalytic reduction of the o-nitrophenylpyrazole 1 results in ring closure to give the pyrazolo[l,5-a]quinoxaline 2. Sequential decarboxylation, treatment with phosphoryl chloride, and catalytic hydrogenation give the parent heterocycle 3. The unsubstituted compound is reported to have a broad band at 240-245 nm in its ultraviolet spectrum in 95% ethanol. A recent patent describes several 4-substituted amino derivatives of pyrazolo[l,5-a]quinoxaline-3-carboxylic acid as possessing antiinflammatory properties. ... 

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