Ultraviolet Spectra Studies

Interesting observations have been made on the ultraviolet spectra of the small-ring organosilicon and other compounds in our various studies. However, only a few selected items will be mentioned here. 

The B bands of the cyclic compounds (Via) and (VIb) exhibit the most dramatic bathochromic shifts, thus suggesting that the deformation of the aromatic nuclei and some transannular interaction of the two aromatic rings is a feature which persists also in the disiloxane-bridged polyhalo-aromatic derivatives of type (VI). The replacement of chlorine for fluorine atoms in the aromatic nuclei also has a pronounced effect upon the ultraviolet absorption spectrum, resulting in a broadening of the B band, disappearance of the fine structure and a strong hypsochromic effect upon the band. 

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The structure of sugar phenylosazones, derivatives first prepared by Fischer in 1884, has remained undefined. Besides Fischer s open-chain structure, a tautomeric azo-hydrazone structure and ring structures have been proposed. Although work in the last two decades involving ultraviolet spectra studies - and examination of the acetylated - and... 

Ultraviolet spectra have long been used to study systems of this type. In 1889, comparison of the ultraviolet spectrum of 2-hydroxy-quinoline with those of its O- and A -methylated derivatives led... 

Attempts have been made to deduce the structure of the predominant form of a potentially tautomeric compound from the shifts which occur in the ultraviolet spectrum of the compound in question on passing from neutral to basic or acidic solutions. The fact that no bathochromic shifts were observed for 2- and 4-hydroxy quinoline and 1-hydroxyisoquinoline under these conditions was taken as evidence that they existed in the oxo form [similar work on substituted quinol-4-ones led to no definite conclusions ]. A knowledge of the dissociation constants is essential to studies of this type, and the conclusions can, in any case, be only very tentative. A further dif-... 

The ultraviolet spectrum of vitamin Be, or pyridoxine, measured in aqueous ethanol varies with the composition of the solvent indicating that this compound is in equilibrium with the zwitterion form 38. The equilibrium constant in pure water was obtained by extrapolation. Prior to this, equilibria which involved tautomers of type 39 had been suggested for vitamin Be, but see Section VI,A. In the case of pyridoxal, an additional equilibrium, 40 41, occurs (cf. Section VIII) other pyridoxal analogs have also been studied (Table II). 

Early investigators adduced various kinds of chemical evidence in support of a monohydroxy-dioxo structure for barbituric acid (112) (a) reaction with diazomethane afforded a mono-O-methyl deriva- iye,i59,i6o barbituric acid and its 5-alkyl derivatives are much stronger acids than the 5,5-dialkyl derivatives, and (c) the 5-bromo and 5,5-dibromo derivatives have different chemical properties. - The early physical evidence also appeared to substantiate the monoenol structure, this formulation having been suggested for barbituric acid in 1926 on the basis of its ultraviolet spectrum and again in 1934, In the 1940 s, ultraviolet spectroscopic studies led to the suggestion of other monohydroxy and dihydroxy structures for barbituric acid, whereas its monoanion was assigned structure 113 (a clear distinction between ionization and tautomerism was not made in these papers). 

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... 

Early attempts to study the structure of thiazol-2-one by comparison of its ultraviolet spectrum with those of both alkylated forms failed because of the similarity of the spectra in the region investigated. However, in 1935, this method was successfully applied to bcnzothiazol-2-one (93) and in 1954 to thiazol-2-one itself,indi-... 

Thus in our study of isotope variations in lengthy chronological sequences of tree rings, we are evaluating fluctuations in the sea surface temperatures, from which distilled the precipitation which nourished the trees and the sea surface temperatures, in turn, are affected by variations in the ultraviolet spectrum of the sun. 

Nuclear magnetic resonance studies on meso-ionic l,2,4-triazol-3-ones (200) were used to examine their relationship to the alternative l,3,4-oxadiazol-2-imine structure (153). The effect of solvent polarity upon the ultraviolet spectrum of anhydro-3-hydroxy-1,4-diphenyl-1,2,4-triazolium hydroxide (200, R = = Ph, R = H) has been discussed... 

Fenter, F. F., V. Catoire, R. Lesclaux, and P. D. Lightfoot, The Ethylperoxy Radical Its Ultraviolet Spectrum, Self-Reaction, and Reaction with HO, Each Studied as a Function of Temperature, . /. Phys. Chem., 97,"3530-3538 (1993). 

Isolation of alkaline phosphatase from Escherichia coli in which 85% of the proline residues were replaced by 3,4-dehydro-proline affected the heat lability and ultraviolet spectrum of the protein but the important criteria of catalytic function such as the and were unaltered (12). Massive replacement of methionine by selenomethionine in the 0-galactosidase of E. coli also failed to influence the catalytic activity. Canavanine facilely replaced arginine in the alkaline phosphatase of this bacterium at least 13 and perhaps 20 to 22 arginyl residues were substituted. This replacement by canavanine caused subunit accumulation since the altered subunits did not dimerize to yield the active enzyme (21). Nevertheless, these workers stated "There was also formed, however, a significant amount of enzymatically active protein in which most arginine residues had been replaced by canavanine." An earlier study in which either 7-azatryptophan or tryptazan replaced tryptophan resulted in active protein comparable to the native enzyme (14). 

Visible-spectrum studies of the course of the dye reduction were performed on a Beckmann Model 25 Ultraviolet-Visible Spectrophotometer scanning the region of 750-350 nm. 

Feitelson obtained good agreement between the ultraviolet spectrum of indolizine calculated from MO theory and the observed spectrum.95 Mason studied the electronic spectra of indolizine and many of its... 

Evidence of intramolecular overcrowding in 3,4-benzophenanthrenes, obtained from the ultraviolet absorption studies, has been discussed by Johnson (1959). It was predicted that the methylene-bridged hydrocarbon, 1,12-methylenebenzophenanthrene (85), should afford the spectrum of a 1,12-dimethylbenzophenanthrene devoid of any steric interference induced by the overcrowded methyl groups. A comparison of the ultraviolet absorption spectra of 1,12-dimethylbenzophenanthrene (83), benzophenanthrene (3), 6,7-dimethylenebenzophenanthrene (84),... 

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. 

The molecule is pyramidal, having C3v symmetry with the nitrogen atom at the apex. The molecular dimensions have been determined by electron diffraction (266) and by microwave spectroscopy (161,271). The molecule with this symmetry will have four fundamental vibrations allowed, both in the infrared (IR) and the Raman spectra. The fundamental frequency assignments in the IR spectrum are 1031, vt 642, v2 (A ) 907, v3 (E) and 497 cm-1, v4 (E). The corresponding vibrations in the Raman spectrum appear at 1050, 667, 905, and 515 cm-1, respectively (8, 223, 293). The vacuum ultraviolet spectrum has also been studied (177). The 19F NMR spectrum of NF3 shows a triplet at 145 + 1 ppm relative to CC13F with JNF = 155 Hz (146, 216, 220,249, 280). 

Treatment of 223 (R1 = R2 = H) with potassium hydroxide and alkyl bromides gave the N- and N,N-disubstituted compounds.261 The reaction of 223 (R1 = R2 = R3 = R4 = H) with methyl iodide and sodium ethoxide gave an N.N -dimethyl compound which on treatment with dilute sulfuric acid and then potassium hydroxide gave 237.265 The ultraviolet spectrum of 223 has been studied but no conclusions have been reached in regard to the tautomerism.281 The... 

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