Ultraviolet comparative

No direct evidence was available at the time of the introduction of the potassium bromide disk method, but attempts to compare spectra of several pyrimidines in terms of the ultraviolet absorption of a KBr disk and an aqueous solution gave support to the inference that there was little or no detectable modification due to the use of potassium bromide. At that time it was thought that the spectrum was, in part, the result of the history of the compound and that changes would be greatest in the ultraviolet spectrum. An additional comparison was made by submitting a common sample of isoguanine for preparation as a vacuum sublimed film. The spectrum obtained in the ultraviolet compared favorably with that obtained with a potassium bromide disk. In attempts to obtain quantitative data, measurements were made to test the validity of Beer s law. However, other workers soon pointed out that the apparent absorptivity is dependent on the particle size of the sample [ ]. The initial work had not indicated this effect since all materials had been... 

Inspect the paper in ultraviolet light—conveniently in front on a Hanovia ultraviolet strip light—in a dark room. The acids show up as intense blue fluorescent spots. Mark with a pencil the positions of all spots. The position of the two spots arising from solution (C) should be compared with the single spots arising from solutions (A) and (B). It is probable that the solution (B) of pure N-methylan-thranilic acid may also reveal a faint spot corresponding to anthranilic acid still present in minute traces in the methylated acid cf. p. 223). 

TABLE 1-19. ULTRAVIOLET ABSORPTION SPECTRA OF THIAZOLIUM TOSYLATES IN EtOH (186) COMPARED WITH CALCULATED TRANSITION ENERGIES (187)... 

The resolution of the ZEKE-PE spectmm of 1,4-difluorobenzene can be compared with, for example, that of the ultraviolet photoelectron spectmm of benzene in Figure 8.12. The greatly increased resolution in the ZEKE-PE spectmm is attributable mostly to the fact that only photoelectrons with zero kinetic energy are being detected. It is also partly attributable to the molecules being in a supersonic jet this has the effect of sharpening the bands because of the restricted rotational populations in the ground state of the molecule. 

Atomic Absorption Spectroscopy. Mercury, separated from a measured sample, may be passed as vapor iato a closed system between an ultraviolet lamp and a photocell detector or iato the light path of an atomic absorption spectrometer. Ground-state atoms ia the vapor attenuate the light decreasiag the current output of the photocell ia an amount proportional to the concentration of the mercury. The light absorption can be measured at 253.7 nm and compared to estabUshed caUbrated standards (21). A mercury concentration of 0.1 ppb can be measured by atomic absorption. 

Comparatively little information is available concerning the use of additives in commercial grades of polycarbonate. Pigments, heat and ultraviolet stabilisers, blowing agents and fire retardants are used but the range of materials available... 

The commercial polymers are of comparatively low molecular weight (M = 25 000-60 000) and whilst being essentially linear may contain a few branches or cross-links arising out of thermal oxidation. Exposure to ultraviolet light causes a rapid increase in gel content, whilst heating in an oven at 125°C causes gelation only after an induction period of about 1000 hours. Eor outdoor applications it is necessary to incorporate carbon black. The polymers, however, exhibit very good hydrolytic stability. 

The infrared, ultraviolet and NMR spectra of /) -octahydro-7-quinoline were compared with the corresponding spectra of the N-ethyl and O-ethyl derivatives in order to determine whether it is in the enamine (64), enolimine (65), or ketimine (66) form. 

The ultraviolet absorption at 222-232 nm is comparable only with immonium structure (186a). No active hydrogen (Zerewitinov) was present in the immonium salts (1,186b) and no deformation vibrations of nitrogen-hydrogen linkage were detected (186a). 

Ultraviolet absorptions ofvinylogous lactams were found by MOLCAO calculations and compared with experimental values (663). Infrared spectroscopic studies of vinylogous amides (664) and some fifty vinylogous urethanes (665) allowed configurational and structural assignments. The effect of enamine-imine equilibrium in a series of benzophenone derivatives was established (666) and the effect of structure on enamine basicity studied (667). 

Many of the properties oj -hydroxypyridines are typical of phenols. It was long assumed that they existed exclusively in the hydroxy form, and early physical measurements seemed to confirm this. For example, the ultraviolet spectrum of a methanolic solution of 3-hydroxypyridine is very similar to that of the 3-methoxy analog, and the value of the dipole moment of 3-hydroxypyridine obtained in dioxane indicates little, if any, zwitterion formation. However, it has now become clear that the hydroxy form is greatly predominant only in solvents of low dielectric constant. Comparison of the pK values of 3-hydroxypyridine with those of the alternative methylated forms indicated that the two tautomeric forms are of comparable stability in aqueous solution (Table II), and this was confirmed using ultraviolet spectroscopy. The ratios calculated from the ultraviolet spectral data are in good agreement with those de-... 

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. ... 

Between 1951 and 1953 investigations by three English groups clearly demonstrated the preponderance of the oxo forms of pyrimidin-2- and -4-ones by comparing the ultraviolet spectra of these compounds with those of the N and 0-alkylated derivatives, The o-quinonoid form 91 (R = H) is favored by the evidence that A -methylation of the 6-methyl derivative of 89a does not cause a bathochromic shift in the ultraviolet spectrum (A -methylation of pyrid-4-one causes a bathochromic shift, but this is not observed for pyrid-2-one) The isomeric A -methyl derivatives of pyrimidin-4-ones [e.g., 91 (R = Me) and 90 (R = Me)] form similar cations (e.g., 92 and 93), and hence the equilibrium constant between... 

Mesomerism involving sulfonyl groups is relatively weak, and in the case of the sulfonyliminopyridones (279) destabilization caused by the factors previously mentioned for the acyliminopyridones should be less important. Early ultraviolet spectral comparisons showed that acetylsulfapyridine and sulfapyridine (cf. reference 354) exist in aqueous solution as mixtures of comparable amounts of 279 and 280. A recent investigation of 2-, 3-, and 4-methanesulfonamido-... 

Tile ultraviolet spectrum of 3-iiitro-l,8-iiaphthyridiiie in methanol A ax [m/A](log e) = 206 (4.06), 238 (4.47), 311 (3.68), and 323 (3.65) showed bathochromic effect of the long-wavelength bands of 10 and 5 m/A with respect to the parent 1,8-naphthyridine (87MI2). Tlie bathochromic effect of 3-nitro group in 1,8-naphthyridine was compared with the effects of some other substituents. 

Benzothiazole-2-thiones are associated,but the predominance of the thione forms (154, R = H, Me) has been demonstrated by ultraviolet spectral comparisons wdth the methylated derivatives of both possible tautomeric forms (cf. reference 182), comparative dipole moment data, and infrared spectral data. " Ultraviolet spectroscopy has also been used to demonstrate that benzoseIenazole-2-thione exists as such. The predominance of the thione form of nonaromatic 3,4-dihydrothiazole-2-ones (155) has also been established on the basis of ultraviolet spectral evidence. ... 

The tautoraerism of certain difunctional derivatives of l-thia-3,4-diazole has received considerable attention. Pala assigned structure 156 to 2,5-dimercapto-l-thia-3,4-diazole on the basis of infrared spectral data, and Thorn" reached the same conclusion by comparing its ultraviolet spectrum (measured in ethanol) with those of the four possible methylated derivatives. However, the infrared spectrum of a chloroform solution of the parent compound showed bands at 2600-2550 cm indicating an SH group and the probable occurrence of form 157 under these conditions, and this conclusion is supported by the occurrence of SH bands in solid state spectra obtained by Swiss investigators. For a summary of earlier work on these compounds, see reference 187. 

The ultraviolet and infrared spectra of 2-aminothiazole and the methyl derivatives of both the imino and the amino forms have been compared and discussed by Sheinker, Kushkin, and Postovskii ° who showed that the amino form predominates in the solid state and in various solvents. The reaction of 2-aminothiazoles with methyl iodide in the presence or in the absence of sodium ethoxide has been considered to give information concerning the proportion of the amino and imino forms present under these conditions, ... 

The structure of 5-amino-l-thia-2,4-diazoles has been clarified by Goerdeler, Huppertz, and Wember who compared the ultraviolet spectra and basicities of 194 (E, = Me or Ph) and the methylated derivatives 195 and 196, thereby showing that 194 exists in the amino form. This conclusion is supported by polarographic data. ... 

Aminoquinoxaline exists predominantly as such rather than in the tautomeric imino form. This is indicated by a comparison of the basic strength of the 2-amino compound (pKo 3.90) and those of its fixed methylated tautomers, 2-dimethylaminoquinoxaline pKa 3.72) and l-methylquinoxalin-2-oneimine (pfCn 8.70). The ultraviolet spectrum of the neutral molecule of 2-dimethylaminoquinoxaline shows the expected bathochromic shifts compared to that of 2-aminoquinoxaline these spectra differ from the ultraviolet spectrum of the neutral molecule of l-methylquinoxalin-2-oneimine (Fig. 1). The mono-cations (68) and (69) derived from 2-aminoquinoxaline and l-methylquinoxalin-2-oneimine have a similar chromophoric system and show almost identical ultraviolet absorption (Fig. 2). 

---