Electronic absorption spectra of styrene heteroanalogs

Conclusions The UV bands for styrene heteroanalogs, as in the case of butadiene heteroanalogs, are shifted toward longer wavelengths upon the introduction of several heteroatoms into one fragment and toward shorter wavelengths upon the introduction of the heteroatoms into different fragments.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2585–2586, November, 1987.     

Electronic absorption spectra of hydrogen bonded amides

The vacuum ultraviolet absorption spectra of various hydrogen bonded amides were measured at various temperatures and concentrations. It was found that the characteristic absorption bands of amides, which appear at 180–190 m, greatly change by hydrogen bonded dimer formation and moreover their changes are sensitive to the relative orientation of the monomers. That is to say, they shift to shorter wavelengths by about 6000 cm^–1 by the hydrogen bonded ring dimer formation and shift to longer wavelengths by about 3000 cm^–1 by the hydrogen bonded chain dimer formation. The theoretical consideration on the energy level splittings due to hydrogen bonded dimer formation explained satisfactorily these observations. The results seem to be important in connexion with the determination of the configurations of polymers which contain peptide bonds as a unit.

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Zusammenfassung Vakuum-UV-Absorptionsspektren verschiedener Amide, die H-Brücken ausbilden, wurden vermessen. Die charakteristische Bande der Amide bei 180–190 m wird durch H-Brücken in Abhängigkeit von der Form des gebildeten Dimeren verschoben: so ist die Verschiebung im Falle der Ringbildung +6000 cm^–1, im Falle linearer Verkettung –3000 cm^–1. Dies Phänomen wird theoretisch erklärt. Die Ergebnisse sind für die Strukturaufklärung von polymeren Amiden von Bedeutung.

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Résumé Les spectres d'absorption U.V. dans le vide ont été mesurés pour différentes amides formant des liaisons hydrogène. La bande caractéristique des amides vers 180–190 m. est déplacée lors de la formation d'une liaison hydrogène: pour des dimères ce déplacement est de +6000 cm^–1 lors de la formation d'un composé cyclique et de –3000 cm^–1 lors de la formation d'un composé linéaire. On explique théoriquement ce phénomène. Les résultats ont une signification pour la compréhension de la structure des amides polymères.

     

Electronic structure and absorption spectra of indolizines

The electronic structure and spectra of indolizine and a large number of its aza-derivatives have been calculated by the SCFMO-CI method, taking into account all the singlet monoexcited configurations. The results are in good agreement with the experiment. The assignment of the observed bands is also discussed.

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Zusammenfassung Mit dem SCFMO-CI-Verfahren werden Elektronenstruktur und Spektren des Indolizins und mehrerer seiner Derivate berechnet, wobei alle einzeln angeregten Singulett-Konfigurationen berücksichtigt werden. Die Ergebnisse stehen in ausgezeichneter Übereinstimmung mit dem Experiment. Die Zuordnung der beobachteten Banden wird diskutiert.

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Résumé La structure et les spectres électroniques de l'indolizine et de plusieurs ses aza-dérivés ont été calculés par la méthode SCFMO-CI, en considérant toutes les configurations singulets monoexcitées. Les résultats sont en bon accord avec l'expérience. L'attribution des bandes observées est aussi discutée.

     

Electronic absorption spectra of some benzenechromiumtricarbonyl derivatives

Absorption spectra of some arenechromiumtricarbonyl derivatives have been studied. The linear dependence of the extinction coefficient of the longer wavelength absorption band on σ_p⁺ constants of substituents in a benzene ring has been established and it has been shown that a longer wavelength band is a band of intramolecular charge transfer from the central chromium atom to π-bonded arene.     

Electronic absorption spectra and EPR spectra of irradiated silicate glasses

The election absorption spectra of sodium silicate glasses in the visible region and the EPR spectra of -irradiated two-component alkali silicate glasses have been studied. It has been established that the electron absorption spectra of these glasses have two bands in the visible region of the spectrum, while the EPR line with g=2.01 consists of two components. A comparison of the absorption spectral data with the EPR spectra showed that the band having a maximum around 4400 å and the -component of the doublet with g=2.01 are associated with the same hole center, of the type Si-O^–... Me⁺ while the band having a maximum around 6200 å and the -component of the doublet arise from a hole center of the type Si-O^–. The change in the ratio of the intensities of the - and -components with changes in the concentration and type of alkali metal is explained.     

Electronic absorption spectra of heteroanalogs of substituted biphenyl

Conclusions It has been demonstrated that Dewar's rule is inapplicable to predictions of absorption band behavior for heteroanalogs of C₆E₅C₆E₄X. A different criterion is proposed, based on the distribution of electron density in the ground and excited states, through which correct predictions can be made.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1770–1772, August, 1987.     

Electronic absorption spectra of merocyanine forms of spiropyrans

A simple method is proposed for the measurement of the absorption spectra in the visible and UV regions of photocolored solutions of spiropyrans, formed by the action of constant lowintensity UV irradiation, and for the construction, on the basis of these data, of the absorption spectra of the merocyanine forms of spiropyrans. The absorption spectra of the merocyanine forms of two spiropyrans in various solvents are examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1534–1538, November, 1972.     

Electronic absorption spectra of selenophene analogs of chalcones

The electronic absorption spectra of 21 1-(selenienyl-2)-3-arylpropen-1-ones and -3-ones are measured in hexane and ethanol solution. It is found that the 2-selenienyl group in such compounds is more bathochromic and electron-donating than 2-furyl and 2-thienyl. The effects of electron-donating and-accepting substituents on _max of a longwave band are considered. It is shown that Hammett's can be connected with shift in absorption frequency when electron-donating substituents are introduced into the aromatic ring of 1-(selenienyl-2)-3-phenylpropen-1-one. The synthesis of three new selenophene analogs of chalcones is described.     

Electronic absorption spectra of selenocarbonyl and thiocarbonyl compounds

Electronic absorption spectra of a variety of thiocarbonyl and selenocarbonyl compounds have been compared to point out their similarities. Interesting correlations between the absorption maxima and electronegativities of substituents in both the seleno- and thio-carbonyl compounds have been reported.     

Electronic absorption spectra of heterocyclic analogs of trans-chalcone

Thiophene, furan, and pyrrole analogs of trans-chalcone have UV spectra consisting of bands belonging to the spectra of the corresponding 2-acetylhetaryls and 2-hetarylideneacetones that are shifted bathochromically as a result of mutual perturbation of these two crossconjugated fragments. The absorption curves of 10 chalcones in hexane solution were measured up to 190 nm, the bands of the individual transitions were isolated graphically, and the degree of localization of the electron excitation on the fragments of the molecules was calculated by a new quantum-chemical method.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1202–1205, September, 1977.     

Electronic absorption spectra of V2O5

MO calculations of electronic structure and optical transitions for [VO_n]^{5 ?; 2n} (n = 4, 5, 6) clusters in V₂O₅ monocrystals have been carried out by means of the semiempirical CNDO CI method. Using the calculated results, a complete analysis of V₂O₅ optical data as available in the literature and as obtained in the electroreflectivity experiments presented in this paper is performed. An identification of optical transitions in a wide energy range is presented. The optical properties of vanadium pentoxide are shown to be due to the localized charge transfer electronic transitions in the clusters. The fine structure of optical spectra is connected with the covalent splittings of the vanadium 3d and oxygen 2p atomic levels.     

Electronic absorption spectra of some arylidene pyrazolone derivatives

The u.v. and visible spectra of some 1 - phenyl - 3 - methyl - 4 - arylidene - 2 - pyrazolin - 5 - one derivatives are investigated in pure and mixed organic solvents as well as in aqueous buffer solutions. Electronic transitions have been identified as either locally excited or predominantly charge transfer states. Moreover, the spectra of the hydroxy derivatives in proton acceptor solvents (DMF, DMSO, ethanol) are characterized by an extra band located at longer wavelengths, which is ascribed to an intermolecular CT transition. This involves an electron transfer from the lone pair of electrons of the oxygen atom of the solvent molecules (ψ_ol) to the antibonding orbital of the substituent OH group. The spectral shifts are discussed in terms of medium effects and in relation to molecular structure. The variation of absorbance with pH is utilized for the determination of pK_a for the dimethylamino and hydroxy derivatives.