Ultraviolet studies

Metal precursor-support interactions in the case of alumina are quite different. The nature of the H2PtClg-Al203 interaction is still open to question. However, recent "in-situ ultraviolet studies (13-14) suggest the following ... 

Infrared Spectrum. The infrared spectrum of gaseous SiF 2 has been recorded from 1050 to 400 cm"1 63 Two absorption bands, centered at 855 and 872 cm 1, were assigned to the symmetric (v j) and antisymmetric (V3) stretching modes, respectively. The assignment was rendered difficult because of the considerable overlap of the two bands. The fundamental bending frequency occurs below the instrumental range of the study, but a value of 345 cm 1 can be determined from the ultraviolet study. The vibrational frequencies were combined with data from a refined microwave study 641 and utilized to calculate force constants and revised thermodynamic functions. 

The ESR spectra of a series of triarylboron anion radicals have been determined and show selective line-broadening effects (95). The radical anions of diborane, generated in an argon matrix at 77 K by irradiation with a-rays have been studied by ESR (121). The vanadium-aluminum complex obtained on mixing dichlorobis(7r-cyclopentadienyl)vanadium with ethylaluminum dichloride, a system that catalyzes the polymerization of ethylene to give a polymer with good characteristics, has been characterized by ESR and ultraviolet studies (44). 

The 1,2-oxides of benzoic acids are also of interest as possible intermediates in the ortho hydroxylation and oxidative decarboxylation of aromatic acids. Ultraviolet studies indicate that benzene oxide 218 predominantly exists as its... 

For 2-imino-4-thiazoline the calculated tt4 — nf transition at 210 nm corresponds to the observed band in thanol at 302 nm (e = 15.000). The localization of this transition (Fig. VI-3) suggests a higher pKa in the tt4 — it excited state for these compounds (63). The Forster cycle, which permits the prediction of protomeric equilibrium for excited states, cannot be applied to the present amino-imino equilibrium because the protonation of 2-aminothiazole may occur on different heteroatoms for ground and excited states. Ultraviolet studies of 2-aminothiazole agree, however, with potentiometric measurements (see Section II.2) that in the ground state the amino form greatly predominates (93). This technique gives the same conclusion in the case of 2-acetamidothiazole (92. 94). 

In another paper Abraham provided a thermodynamic analysis that placed f-Bu Cl and the separated ions at about the same free energy, 14.5 kcal/mol above the reactant. This implies a AG of about 5 kcal/mol for collapse of the contact ion pair back to reactants, although the uncertainties in Abraham s analysis are at least 5 kcal/mol. Few related data are available, except some dynamic NMR results for the collapse of trityl and tropylium chloride ion pairs. " In both the NMR work and Abraham s analysis, solvent-separated ion pairs are not included as distinct entities. However, the interconversion of contact and solvent-separated ion pairs has been observed in ultraviolet studies of delocalized carbanions in THF. ... 

Since the insolubility of the solid polymer precluded any ultraviolet studies in solution, attempts were made to obtain a diffuse reflectance spectrum of the solid. Meaningful data could not be obtained. Again, however, the liquid polymer could be compared with authentic polystyrene. Figure 4 shows the ultraviolet spectra of the two materials. Although the resolution is poor for the liquid polymer, its spectrum generally agrees with that of polystyrene. 

Calculations, by variable integral methods, of n-n transitions for indoxazenes are in good agreement with experimental data.38 Ultraviolet spectra of 3-hydroxyindoxazenes and of several indoxazene-3-carboxylic acids are available.8,23 On the basis of ultraviolet studies it is concluded that indoxazenes are weaker bases than the corresponding isoxazoles.39 Similar... 

In aqueous solution the cations of the parent heterocycle and its 2-methyl and 2,3-dimethyl derivatives are covalently hydrated. The neutral molecules are anhydrous. The tri- and tetramethyl derivatives are not hydrated either as neutral species or as cations. These conclusions were reached on the basis of acidity constant measurements and ultraviolet studies and confirmed by PMR spectroscopy. The PMR spectra show that hydration occurs by the addition of two molecules of water to give cations of formula 4. Substitution by a methyl group at either of the sites of hydration renders the cation completely anhydrous. Moreover the introduction of methyl groups to give compound 4 (R = Me) reduces the extent of hydration. Thus the cations of pyrazino[2,3-h]pyrazine and its 2-methyl derivative are completely hydrated in aqueous solution, whereas the protonated 2,3-dimethyl compound exists as a 3 1 mixture of the dihydrate and the anhydrous species. 

The combination of infrared and visible-ultraviolet studies of any system has certain obvious advantages. For example, if chemisorbed olefins on a supported metal catalyst are partially hydrogenated to form free radicals, the combined ir and uv can completely define the species. The ir is capable of determining the kind of groups present and the free electron will have a unique absorption band somewhere in the visible-ultraviolet region. 

The experimental conditions for the vacuum ultraviolet study were chosen so that the vibrational relaxation process was short and complete with respect to the observation times. The rate coefficients were calculated from an analysis of the initial slope of the absorption trace over a temperature interval of 8000—15,000°K. These high temperatures necessitated consideration of the cooling of the shocked gas due to thermal ionization of the diluent. It was concluded that even at a temperature of 15,000°K, the effect on the initial rate data was negligible. 

Kishi, K., Ikeda, S., and Hirota, K. (1967) Infrared and ultraviolet studies of the adsorption of acetylaeetone on evaporated iron and nickel films, J. Phys. Chem. 71, 4384 - 4389. 

Ninomiya, T., Kishi, K., and Ikeda, S. (1970) Ultraviolet study for the adsorpton of acetylacetone on D-tartaric acid preadsorbed nickel film. Bull Chem. Soc. Jpn. 43,2270. 

Tautomeric equilibrium constants Kf = [pyridone]/[pyridinol] have been measured for a number of 2-pyridones (Table XII-8). The constant Kf has been estimated by a Hiickel approximation for 2- and 4-pyridone. The Kf values obtained from ultraviolet spectra and those obtained from acidity constants are in poor agreement for 6-chloro-4-substituted-2-pyridones (XII477 R = CH3, CeHs) and 6-chloro-3,4-polymethylene-2-pyridones (XII-478 n = 3,4) in water. For example, in XII477 where R = CH3, values of 6% and 44%respec-tively of pyridinol tautomer (XII477b) are obtained from ultraviolet data and from acidity constants. However, values obtained from ultraviolet studies appear to be more reliable. ... 

Ultraviolet study of complexing agents in a polynitroaro-matic compound... 

Zingaro, R.A., McGlothlin, R.E. and Meyers, E.A. (1962) Phosphine oxide, sulfide, and selenide complexes with halogens visible and ultraviolet studies. J. Phys. Chem., 66, 2579-2584. 

Some of the unmanned satellites primarily dedicated to UV solar or celestial astronomy include the Solar Maximum Mission (SMM), the International Ultraviolet Explorer (lUE), the Extreme Ultraviolet Explorer (EUVE), the Far Ultraviolet Spectroscopic Explorer (FUSE), and the Solar Heliospheric Observatory (SOHO). Ultraviolet studies of the sun are also a significant part of the Upper Atmospheric Research Satellite (UARS) mission, andUV astronomy is an important part of the operations of the Hubble Space Telescope. 

It is now clear that an earlier ultraviolet study of acetone as an indicator (257) arrived at a misleadingly high basicity for acetone through failure to cover a wide enough range of acidities and to make proper allowance for solvent shifts. Unfortunately, this wrong value for the pKa was employed in a kinetic treatment of the acid-catalyzed bromination of acetone (4) which must now be reconsidered (61). 

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