UV spectroscopic study

Early IR- and UV-spectroscopic studies [76AHC(S1), p. 481] of 5-amino-l,2,4-thiadiazolin-3-one and 5-amino-l,3,4-thiadiazolin-2-one indicate structures 236 and 237, respectively. 

Photo-Fries Rearrangement of Styrylpyridine Based Ester and Carbonate-UV-Spectroscopic Studies... 

UV spectroscopic studies of chlorpromazine hydrochloride were conducted in ethanol and water solutions, and the resulting spectra are shown in Figure 3. The data were obtained between 200 and 345 nm using a Shimadzu 1601 PC UVA IS spectrophotometer (Figure 3). 

All UV spectroscopic studies (e.g., refs. 105, 106, 340) show that at pH >13 uracil and its C-substituted derivatives are best described by the dianionic structure 41 with the negative charges localized on both oxygens. 

As was mentioned already, 3- and 6-phenyl substituted l,2,4-triazin-5-ones exist in the solid state as the 5-hydroxy tautomers, as was shown by IR spectroscopy (74T3171). From UV spectroscopic studies it was suggested that the zwitterionic 2-methyldihydro-l,2,4-triazinium-6-olates (48a) are better formulated as such, rather than as the tautomeric alternatives (48b, 48c) (78JHC1271). 

The early spectroscopic studies using IR (Chelton and Traxler, 1957) and nuclear magnetic resonance (NMR) (Williams, 1959) observed both aromatic and alkyl structures in asphaltenes. Visible-UV spectroscopic studies by Erdman et al. (1958) indicated that asphaltenes and resins from the same petroleum source have a similar chemical structure but that significant variations existed among different petroleums. This is consistent with the observation that the resin-asphaltene interaction is specific in that the resins from one petroleum do not readily solubilize the asphaltene from another petroleum (Koots and Speight, 1975),... 

A UV-spectroscopic study of 5-bromo-4-nitroimidazole is said to demonstrate that charge is localized on the peripheral heteroatom rather than on the heteroannular nitrogen. Ultraviolet spectroscopy has been applied to studies of 2,4,5-triarylimidazolyl radicals, 1-arylimidazoles, and... 

Experimental data concerning protonation sites for monocyclic 1,2,4-triazines are still not sufficient to make any generalization of this phenomenon. On the basis of ultraviolent (UV) spectroscopic studies it has been... 

Similarly to 3-hydroxypyridines, 5-hydroxypyrimidines can potentially exist in neutral form 56a or in zwitterionic form 56b. The UV-spectroscopic studies of these compounds in aqueous solution showed that the parent compound (R1 = R2 = H) exists in acidic medium (pH 3.1-4.3) as a mixture of both forms in ratio 56a 56b = 50 1. The introduction of methyl groups (R1 or R2 = Me) shifts the equilibrium toward the bipolar form 56b, although 56a still predominates. The introduction of a phenyl group into the position 2 induces the opposite effect (89KG1094). 

For estimation of the 2-(l //)-pyrazinone/2-hydroxypyrazine equilibrium in a solution, the 13C,111 spin-spin coupling constants were applied, and the results were supported by 15N NMR data. The oxo tautomer 57a was found to be the dominant species both in DMSO-d6 and CD3N02 with the molar ratio 57a 57b being ca. 9 1 in DMSO-4 (82TF4785). UV spectroscopic studies indicate the predominance of the hydroxy form for 2-hydroxy-6-methoxypyrazines 58 (R1, R2 = Me, Ph)... 

According to UV spectroscopic studies, 3-hydroxypyridine 1-oxide exists in ethanol, and aqueous acidic and alkaline media in forms 142a, 142b, and 142c, respectively. No bipolar form 142d has been detected (74KG92). The relative stabilities of tautomers of... 

Detailed UV spectroscopic studies on the deep colored dimers (34) and related compounds have been published. The visible and UV absorptions of derivatives with various ethylene chains have been compared <86KGS1693,88KGS418>. 

Overexchanged versus Underexchanged Cu-ZSM-5. In their study on direct NO decomposition, Iwamoto et al found that the catalytic activities of Cu-ZSM-5 increase with copper ion exchange level and level off over 100% exchange capacity(7). This observation was confirmed by Li and Hall in their kinetics study(T). They also observed that oxygen desorption rate for Cu-ZSM-5-166 is higher than that of Cu-ZSM-5-76. From the exchange site distance analysis and UV spectroscopic study, Iwamoto et aL proposed that a dimeric copper species, possibly in the form of Cu -O -Cu, is the precursor for auto-reduction of the complete redox cycle. 

This reaction mechanism was first proposed by Halsted and Thrush (30) when studying the kinetics of elementary reactions involving the oxides of sulfur. Visible and UV spectroscopic studies (31) confirmed that the chemiluminescent emission was from SO2. Recently, it has also been confirmed that the sulfur- analyte molecule from the GC effluent is converted to SO in the flame of the SCD (32). Even though SO is a free radical, it can be sufficiently stabilized in a flow system under reduced pressure (33,34) to be sampled and transferred to a vessel to react with introduced O. Based on these operational principles. Burner and Stedman (33) concluded that SO produced in a flame could be easily detected. They modified a redox chemiluminescence detector (36) to produce what was termed a Universal Sulfur Detector (USD). A linear response between 0.4 ppb and l.S ppm (roughly equal to 3 to 13,000 pg of S/sec) was demonstrated with equal response to the five sulfur compounds tested. This detection scheme has been utilized as the basis for the commercially available GC detector. 

The UV spectroscopic study revealed that a molar absorption coefficient of a fullerene Cg and several synthesized methanofullerenes does not depend on the solvent and functional group nature but hinges on the number of substituents. Moreover, as their number increases, the molar absorption coefficient decreases by the exponential law. 

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