Ultraviolet-visible amines

The ultraviolet-visible spectra of both PDA—H and PDA- apparently have a common band (3, = 295 nm (15 700) 296 (16 700)), the so-called amine tt-conjugation band (p. 411), involving the nitrogen lone electron pair (Ballester and Riera, 1967). Two additional bands are found in PDA-(470 nm (2300) 665 (425)), which are inherent to the radical character, much like the two observed in PTM radicals (380, 500-560 nm) (p. 419) (Olivella, 1973). Because of these features, it is concluded that each of the two nitrogen nonbonding orbitals interacts strongly with both pentachlorophenyl Jt-systems, and therefore they are nearly equivalent. Consequently, efforts to identify the semioccupied orbital (Walter, 1966), might be pointless, at least in PDA-. 

It has been found that (i) the hydroxylamine [136], under the same conditions, gives a deep-blue solution (with ultraviolet-visible spectrum almost coincident with that of the solution from radical PDNO ), which after hydrolytic treatment affords the quinonimine [137] (84%), the diphenyl-amine [138] (12%) and PDNO- (4%) (ii) the oxammonium ion [140] can be... 

After separation of the insoluble fraction the nitroformaldehyde arylhydrazone was precipitated with dilute hydrochloric acid (0.25 M), Three such cleaning cycles were required to obtain reasonably pure product The reaction yield was 42% bakd on the amine used in the synthesis. Air (tied solid nitroformaldehyde p-naphthylhydrazone is orange and melts at 90-94T. It was characterized by infrared and ultraviolet-visible spectroscopy. 

Composite resins can be cured using a variety of methods. Intraoral curing can be done by chemical means, where amine—peroxide initiators are blended in the material to start the free-radical reaction. Visible light in the blue (470—490 nm) spectmm is used to intraoraHy cure systems containing amine—quin one initiators (247). Ultraviolet systems were used in some early materials but are no longer available (248). Laboratory curing of indirect restorations can be done by the above methods as well as the additional appHcation of heat and pressure (249,250). 

The focus of the earlier chapter was a brief outline of the sources of chiral amino compounds, application of Brewster s rules for the assignment of the absolute configurations to a few chiral amines, a discussion of the ORD and CD in the visible (380-780 nm) and near-ultraviolet (200-380 nm) spectral regions of chiral amino compounds and some of their derivatives, and how the observed Cotton effects (CEs) in their ORD curves and CD spectra relate to their conformational preferences and absolute configurations. 

The triacetate uranyl complex (24) is structurally similar to the trinitrate uranyl complex (6) (three bidentate ligands arranged equa-torially around the uranyl O—U—O axis). It was expected that the visible, near ultraviolet spectrum of the triacetate uranyl complex would be similar to the spectrum of U02(N03)3 as are the spectra of 1102(804)3, 1102(003)3 , and other uranyl complexes which apparently have the same structure (17). The absorption spectrum of uranyl acetate extracted into tri-n-octylamine in xylene from dilute acetic acid is different from the trinitrato uranyl spectrum. This indicates that the triacetate uranyl complex is probably not the species involved. By analogy to the uranyl nitrate system 14), formation of a tetraacetate uranyl complex might be expected. The purpose of this work is to determine the nature of the anionic hexavalent actinide acetate complexes and to identify the species involved in the amine extraction and anion exchange of the hexavalent actinides from acetate systems. 

Such aromatic amines and diamines, as diphenylamine, iV-methyl-diphenylamine, triphenylamine, benzidine, p-phenylenediamine, etc., are known to have low ionization potentials (75) and to yield univalent positive molecular ions (semiquinones) under ultraviolet irradiation in rigid media (76), or by oxidation in solutions (77). These molecular ions possess characteristic absorption bands in the visible range. 

The adsorption of the vapors of these amines in vacuo on carefully degassed silica gel, or porous glass at temperatures, ranging from 20 to 100°C does not produce any visible coloration of the adsorbent. The absorption spectrum reveals only the normal ultraviolet bands of the adsorbed molecules at 280-300 m/j,. However, the adsorption of the same vapors on carefully degassed and evacuated silica-alumina invariably produces a more or less strong coloration of this adsorbent, the spectrum of which reveals bands undoubtedly belonging to the positive ion-radicals of the adsorbed molecules (27, 77a). 

While there are obvious ultraviolet (UV) changes simply upon addition of SO2 to an amine, incorporating the porphyrin in the assay brings the response into the visible region of the spectrum. It should be possible to modify both amines and porphyrins to achieve more colorful responses, and also to detect SO2 in aqueous solutions and at the gas-solid interface. 

The simplest method for the determination of amino acids is reaction with ninhydrin. Ninhydrin reacts with both primary and secondary amino acids to produce Ruhemann s purple, which can be detected by ultraviolet (UV)-visible spectroscopy. The reaction requires heat, and a reducing agent is generally added to stabilize the color formation. Primary amines are detected with the greatest sensitivity at 570 nm, while the absorption maximum for secondary amines is 440 nm. If both primary and secondary amines are to be determined, a common absorption wavelength of 500 nm is employed however, this leads to decreased sensitivity. Under optimal... 

Spectrophotometry in the ultraviolet (UV) range has repeatedly proven to be a fast, inexpensive and reliable method for the monitoring of many compounds in urban and industrial wastewaters (Narayana and Sunil 2009 Pinheiro et al. 2004). Through the application of spectral analysis, quantitative and qualitative wastewater parameters can be estimated on direct samples in just a few minutes, using portable or online field instrumentation. Perez (2001) has successfully applied UV spectral deconvolution on wastewater monitoring in a chemical industry, for the estimation of aniline derivative concentrations. In the case of textile effluents, the use of the UV range of the spectra (200-350 nm) for aromatic amine determination is particularly useful to avoid interference by visible colour of dyes. The characteristic... 

Detection of / -aminobenzenesulfonamide derivatives is similar to that of aromatic amines, either with / -dimethylaminobenzaldehyde (p. 349), or by diazotization with vapors of nitrogen oxides and coupling (p. 349). Roux reagent is also suitable 10 g of sodium nitroprusside are dissolved in 100 ml of water, and the solution is mixed with 2 ml of 33% NaOH and 5 ml of 0.1 N KMn04, and is filtered after spraying the paper, spots of various colors appear, which are observed in visible or ultraviolet light. 

Ogawa, Y., Iwasaki, S., and Okuda, S., Photochemical aromatic hydroxylation by aromatic amine N-oxides, remarkable solvent effect on the NlH-shift, Tetrahedron Lett., 22, 3637, 1981. Botchaway, S.W., Chakrabarti, S., and Makrigiorgios, G.M., Novel visible and ultraviolet light photogeneration of hydroxyl radicals by 2-methyl-4-nitroquinoline N-oxide (MNO) and 4,4 -dinitro-(2,2 )bipyridyl N,N -dioxide (DBD), Photochem. Photobiol, 67, 635, 1998. 

The principal difference between the two systems is in the way in which the free radical polymerization of the methacrylate monomers is initiated. In one, it is accomplished photochemically (with either ultraviolet or visible light) and in the other it is accomplished chemically with a standard amine-peroxide system. 

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