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 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 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 structure and electronic absorption spectra of molybdenum and tungsten oxotetrachlorides

Electronic absorption spectra of the molecules MoOCl₄ and WOCl₄ have been measured and their electronic structure has been calculated on the basis of the SCF-X-SW theory in the overlapping atomic sphere model. Ionisation potentials and allowed optical transition energies have been found in the transition state approximation. The interpretation of the electronic absorption spectra of gaseous MoOCl₄ and WOCl₄ is given.     

Electronic structure and absorption spectra of dicarbonium ions containing bridging groups

The electronic structure and spectral characteristics of polymethines with the general formulas [CH₃-M-C₆H₄-(CH)_n-C₆H₄]⁺ X^– (C) and [R-C₆H₄-(CH)_n-C₆H₄-M-C₆H₄-(CH)_n-C₆H₄-R]²⁺ 2X^– (D) were investigated. The absorption spectra of the dicarbonium ions were treated in terms of the theory of intramolecular interaction of the chromophores. By analysis of the experimental data and calculated data, obtained by the PPP method, it was established that the long-wave splitting in compounds of type D increases in the series M= (CH₂)₂ CH₂, O, S, NCH₃, does not depend on the electronic symmetry of the parent compounds (C), decreases with increase in the length of the polymethine chain (n), and decreases with increase in the electrondonating characteristics of the substituents (R). The energy of intramolecular interaction of the chromophores is separated into dipole-dipole, resonance, and exchange components, a method is proposed for their quantitative assessment, and the effect of various structural factors on them is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 419–427, July–August, 1988.     

Electronic absorption spectra of the cations and anions formed from pyrrole analogs of the chalcones

The electronic absorption spectra of 29 pyrrole analogs of the chalcones have been studied in solutions of strong acids and alkalies, in which the corresponding cations and anions are formed. It has been shown by means of the IR spectra that the protonation of the pyrrole chalcones takes place at the carbonyl group. Considerations are given of the structure of the organic cations and anions studied and of the characteristic features in the change in their coloration as a function of their chemical structure. Satisfactory correlations have been found between the shift of the absorption frequency of the long-wave band which takes place at the transition from a neutral solution (molecules) to an acid solution (cations) or to an alkaline solution (anions) and Hammett's o constants. Three 3-(4-halophenyl)-1-(2-pyrryl)propenones not previously reported in the literature have been synthesized.     

Electronic absorption spectra of the cations and anions formed from pyrrole analogs of the chalcones

The electronic absorption spectra of 29 pyrrole analogs of the chalcones have been studied in solutions of strong acids and alkalies, in which the corresponding cations and anions are formed. It has been shown by means of the IR spectra that the protonation of the pyrrole chalcones takes place at the carbonyl group. Considerations are given of the structure of the organic cations and anions studied and of the characteristic features in the change in their coloration as a function of their chemical structure. Satisfactory correlations have been found between the shift of the absorption frequency of the long-wave band which takes place at the transition from a neutral solution (molecules) to an acid solution (cations) or to an alkaline solution (anions) and Hammett's o constants. Three 3-(4-halophenyl)-1-(2-pyrryl)propenones not previously reported in the literature have been synthesized.     

Electronic structure and absorption spectra of yttrium quinaldinates with an island and polymer structure

The electronic absorption spectra and electronic structure of yttrium quinaldinates with an island and polymer structure were studied. A comparative analysis of the energies of the singlet and triplet excited states, the total energies of complex compounds in the ground state, and Mulliken’s bond overlap populations was performed by the TD-DFT method with the B3LYP density functional. For yttrium quinaldinate with a polymer structure, the distance between the highest occupied and lowest unoccupied orbitals was found to be longer than for the compound with an island structure. The transition energies were shifted to the blue region, which accounts for the higher stability of the polymer compound.     

Electronic structure and absorption spectra of a dimeric tantalum (III) compound and its transient anion

Relativistic MS Xα calculations have been performed on Ta₂Cl₆(NH₃)₄ and [Ta₂Cl₆(NH₃)₄]⁻. These complexes have been chosen as models for Ta₂Cl₆(γ-pic)₄ and the short-lived anion generated by pulse radiolysis reduction of the neutral species. A comparison of the calculated electronic transitions and the experimental data leads to the conclusion that the transient Ta dimer has a formal bond order of 1.5 (electronic configuration σ²π²δ). This result is related to experimental observations.     

Electronic absorption spectra of benzoquinone and its hydroxy substituents and effect of solvents on their spectra

The electronic absorption spectra of 1,4-benzoquinone (BQ) and its 2,5-dihydroxy and tetrahydroxy derivatives have been studied in detail. The interpretation of the electronic bands is made on the basis of PPP and CNDO calculations. It is found that the pi --> pi* transitions are well predicted by the PPP method. The predictions of the CNDO method are however superior both in their accuracy as well as ability to predict the n --> pi* transitions. The effect of solvents on the electronic absorption bands have also been investigated in detail. Linear correlations are found between the solvent's dielectric constant and wavelength of the absorption bands. The solvent shifts are explained on the basis of the polarities of the solute and solvent molecules as well as due to hydrogen bonding.     

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 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.