Ultraviolet spectra of solutes

The ultraviolet spectra of solutions of potassium nitrate in various concentrations of sulphuric acid have been studied, and absorptions... 

PH Hg presence11 Irradiation11 period min Ultraviolet spectra of solutions ... 

An intramolecular charge transfer toward C-5 has been proposed (77) to rationalize the ultraviolet spectra observed for 2-amino-5-R-thiazoles where R is a strong electron attractor. Ultraviolet spectra of a series of 2-amino-4-p-R-phenylthiazoles (12) and 2-amino-5-p-R-phenylthiazoles (13) were recorded in alcoholic solution (73), but, reported in an article on pK studies, remained undiscussed. Solvent effects on absorption spectra of 2-acetamido and 2-aminothiazoles have been studied (92). 

A number of bridged crown ethers have been prepared. Although the Simmons-Park in-out bicyclic amines (see Sect. 1.3.3) are the prototype, Lehn s cryptands (see Chap. 8) are probably better known. Intermediates between the cryptands (which Pedersen referred to as lanterns ) and the simple monoazacrowns are monoazacrowns bridged by a single hydrocarbon strand. Pedersen reports the synthesis of such a structure (see 7, below) which he referred to as a clam compound for the obvious reason . Although Pedersen appears not to have explored the binding properties of his clam in any detail, he did attempt to complex Na and Cs ions. A 0.0001 molar solution of the clam compound is prepared in ethanol. The metal ions Na and Cs are added to the clam-ethanol solutions as salts. Ultraviolet spectra of these solutions indicate that a small amount of the Na is complexed by the clam compound but none of the Cs . 

Recently, many investigators have extended the early observations that the ultraviolet spectra of - and y-hydroxypyridines resemble those of their A -methyl (not the 0-methyl) derivatives. This spectral resemblance is found both in aqueous solutions and in solutions of solvents with low dielectric constants, e.g., quinol-4-one in benzene, indicating that these compounds exist predominantly in the oxo form under all conditions. These data are summarized in Table I. In contrast, 4-hydroxyquinoline-3-carboxylic acid has been tentatively concluded to exist in the hydroxy form %- pjTid-2-one-4-carboxylic acid has also been formulated as a hydroxy compound, but this has been disputed. ... 

The pKa values of 4-hydroxypyridine 1-oxide (51 52) and the methylated derivatives of both tautomeric forms indicate that the parent compound exists as a mixture containing comparable amounts of both forms in aqueous solution. Nuclear magnetic resonance spectra support this conclusion, but the ultraviolet spectra of the tautomeric compound and both alkylated derivatives are too similar to give information concerning the structural nature of the former. ... 

There is a discrepancy in the literature concerning 4-hydroxy-cinnoline. Whereas two measurements of pKa values indicate that the cinnolinone structure predominates by a large factor in aqueous solution (see Table III), comparison of the ultraviolet spectra of 4-hy-... 

These compounds usually give many of the reactions characteristic of phenols and were long considered to exist completely in the hydroxy form (see, for example, reference 42). It has been noted that the ultraviolet spectra of aqueous ethanolic solutions of hydroxy-acridines varied with changes in the composition of the solvent, and this phenomenon has been interpreted in terms of the equilibria 132 133 and 134 135. Some compounds of these types show... 

Comparison by Gardner and Katritzky of the pKa values of the cations formed by 2- and 4-aminopyridine 1-oxide and the alkylated derivatives of both forms showed that in aqueous solution the amino form predominates for 2- and 4-aminopyridine 1-oxide (cf. 241 242) and the methylamino form for 2- and 4-methylaminopyridine 1-oxide by factors of ca. 10 and >10 in the 2- and 4-series, respectively. The ultraviolet spectra of the 4-isomer and its alkylated derivatives... 

The ultraviolet spectra of the pyridinecarboxylic acids (334) were initially interpreted assuming that the proportion of the zwitterion structure 335 was not appreciable,and the early pK work was inconclusive. However, Jaffe s calculations based on the Hammett equation indicated that about 95% of nicotinic and isonicotinic acids existed in the zwitterion form, and ultraviolet spectral data showed that the actual percentages of picolinic, nicotinic, and isonieotinie acids existing in the zwitterion form in aqueous solution are 94, 91, and 96%, respectively.This was later confirmed by Stephenson and Sponer, who further demonstrated that the proportion of the zwitterion form decreases in solvents of low dielectric constant, becoming very low in ethanol. Dipole moment data indicate that isonicotinic acid exists as such in dioxane, and 6-hydroxypyridine-3-carboxyiic acid has been shown to exist in form 336 u.sing pK data. ... 

Macbeth and Price- have shown that in ethanolic solution the tautomeric equilibrium between 225 and 226 is about 80% in favor of the hydroxy form (225) when R is H and that the equilibrium is shifted still further toward the hydroxy form when R is NO2 by comparison of the ultraviolet spectra of the parent compounds and... 

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... 

Ultraviolet Spectra of Nitric Acid Solutions , CanJRes 27B, 580-603 (1949) 28) J.H. 

Ultraviolet spectra of diazonium salt solutions were recorded for the first time by Hantzsch and Lifschitz as early as 1912. However, electron spectra did not provide significant information on the structure of diazonium ions, either at that time or later. For example, Anderson and coworkers (Anderson and Steedly, 1954 Anderson and Manning, 1955), compared spectra of 4-amino-benzenediazonium salts with those of diphenylquinomethane (4.18). Their conclusion that the structures of these compounds are analogous is basically correct, but the arguments given by Anderson can easily be refuted, as shown by Sorriso (1978, p. 102). 

There is a rich literature on preparative electrochemical reductions of halosilanes. Dessy et al. reported that Ph3SiH was formed by the electrochemical reduction of Ph3SiCl in 1,2 dimethoxyethane (DME) using a dropping mercury cathode at - 3.1 V vs. AgClOJAg [80]. Although the ultraviolet spectra of the solutions after electrolysis were identical with the spectra of an authentic sample of Ph3SiH, the product was not isolated. 

Ultraviolet spectra of compounds are usually determined in the vapour phase or in very dilute solution. The most commonly used solvents in u.v. studies are cyclohexane, 95% ethanol and 1 4 dioxane. The most widely used is 95% ethanol because it is cheap, good solvent and is transparent down to about 210 nm. It is also a good choice when a more polar solvent is required. The most useful solvent would be that which would not absorb within the region under investigation. 

A number of investigators have studied the effect of ozone on the ultraviolet absorption spectra of proteins and amino acids. A decrease in the absorption of 280-nm light in a number of proteins was originally reported ly Giese et aV to be a consequence of ozone exposure they suggested that this was due to an interaction of ozone with the ring structures of tyrosine and tryptophan. Exposure of a solution of tryptophan to ozone resulted in a decrease in 280-nm absorption, whereas the extinction coefficient of tyrosine increased. Similar results with tyrosine were reported by Scheel et who also noted alterations in the ultraviolet spectra of egg albumen, perhaps representing denaturation by ozone. 

Ultraviolet spectra of benzoic acid in sulphuric acid solutions, published by Hosoya and Nagakura (1961), show a considerable medium effect on the spectrum of the unprotonated acid, but a much smaller one in concentrated acid. The former is probably connected with a hydrogen-bonding interaction of benzoic acid with sulphuric acid which is believed to be responsible for a peculiarity in the activity coefficient behaviour of unprotonated benzoic acid in these solutions (see Liler, 1971, pp. 62 and 129). The absence of a pronounced medium effect on the spectra in >85% acid is consistent with dominant carbonyl oxygen protonation. In accordance with this, Raman spectra show the disappearance in concentrated sulphuric acid of the carbonyl stretching vibration at 1650 cm (Hosoya and Nagakura, 1961). Molecular orbital calculations on the structure of the carbonyl protonated benzoic acid have also been carried out (Hosoya and Nagakura, 1964). 

The ultraviolet spectra of the precipitate can be seen in Figure 2 along with the spectra of pure caffeine and pure pyrogallol solutions. With such low concentrations it is assumed that the caffeine and pyrogallol are completely dissociated and that their ultraviolet spectra will be additive. Hence, if we let the ratio of pyrogallol with respect to caffeine be 1 P, then the extinction coefficient of the complex is ... 

The ultraviolet spectra of the several epiuulfides studied3 in both solution and in the gas phase are characterized by one band in the region of 2600 A (38,460 om. 1). Studies have been made on ethylene sulfide, propylene sulfide, and cyclohexane sulfide. The /solution spectra have inflections in the region of 2450 A (40,820 cm.-1). The gaa-phase spectrum reveals a distinct second transition... 

Phenolic Hydroxyl Group. An ethanolic solution of 3,4,5-tri-methoxybenzyl alcohol (4-0-methylsyringyl alcohol) and sodium hydroxide was prepared, and ultraviolet spectra of the solution were recorded immediately and 3 days after preparation. These spectra were compared with the spectrum of the model compound in neutral ethanol. The three spectra were identical with the absorption curve possessing a broad maximum in the 270-280 m/x region. Further visual observation of the alkaline solution for 2 weeks revealed no color formation. This suggests that phenoxide ion formation may be a necessary initial step in reactions leading to the development of chromophoric structures from lignin model compounds. 

After this reference compound and reaction product were eluted with water from the chromatogram, their neutral spectra were recorded. In addition, the neutral spectrum of an aqueous 2,6-dimethoxyquinone solution was obtained the locations of the maxima of the three spectra are given in Table III which shows that the ultraviolet spectra of the three compounds in aqueous solution possessed maxima at the identical wavelength of 289 mp. 

The carbonyl group. Acetone (in cyclohexane solution) exhibits two absorption bands one appears at 190nm (e 1860) and corresponds to the n - n transition, while the second is at 280 nm (e 13) and corresponds to the n - n transition. The absorption maxima of these bands are solvent-dependent. Ultraviolet spectra of saturated aldehydes, carboxylic acids, esters and lactones exhibit a similar absorption profile, and in general are of little diagnostic value. 

Fig. 4. Ultraviolet spectra of H3SbS and lt3SbX2. Dashed curve, in n-hexane solid curve, in acetonitrile. (1) (CH3)3SbS (Xma, 279 nm, because of its poor solubility, the supernatant solution obtained after shaking for 30 minutes was used) (2) (CH3)3SbS (1.10 X 1 fl 1 mole/liter, Xmax 267 nm, log e 3.6) (3) (C Hn) SbS (0.893 X 10-4 mole/ liter, Xmax 282 nm, log 6 3.7) (4) (CeHubSbS (0.839 X 10-4 mole/liter, Xmax 274 nm, log 3.8) (5) (CH3)3SbCl2 (1.27 X HU4 mole/liter) (6) (CH3)3SbBr2 (1.06 X lO"4 mole/liter) (7) (C Hn)3SbBr2 (1.01 X 10-4 mole/liter).

Fig. 4. Ultraviolet spectra of species found in acid (pH < 7) vanadate(V) solutions. Wavelength range is 250-390 nm. Reprinted with permission from Ref. 24...

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