Substitution effect in electronic absorption spectra of 2- and 2,6-substituted 4-benzhydrylidene-2,5-cyclohexadien-1-ones

1984 ◽  
Vol 49 (9) ◽  
pp. 1949-1964 ◽  
Author(s):  
Lubomír Musil ◽  
Bohumír Koutek ◽  
Jiří Velek ◽  
Milan Souček
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Significant Contribution ◽  
Inductive Effect ◽  
Electronic Absorption Spectra ◽  
Resonance Effect ◽  
Gaussian Function ◽  
Substitution Effect ◽  
Band Position ◽  
Wavelength Absorption

Electronic absorption spectra of the seventeen fuchsone derivatives Ia-Iq were recorded in n-hexane. The symmetric Gaussian function could be fitted to absorption profiles within the region of the lowest energy π-π* transition. Bad parameters obtained in this way were utilized in calculation of the corresponding oscillator and dipole strengths. The effect of substitution on positions and intensities of all the observed bands was also investigated. The most sensitive response to substituent change is exhibited by the longest wavelength absorption band. The relation between the substituent nature and band position or oscillator strength may be quantified as P sum from i=1 to n (ρiσi) + P0. It follows from the analysis of variance that both the inductive and steric effects are operating. On the other hand, for the non-symmetrically substituted fuchsones, the band intensity characterized by the molar absorption coefficient is a linear function of the inductive effect only. There is no statistically significant contribution of the resonance effect in any of the quantities investigated. The effect of solvent was followed by the separate evaluation of the wavenumbers related to maxima of the longest wavelength band of fuchsones Ia-Iq in the following series of solvents: n-hexane, cyclohexane, isooctane, tetrahydrofurane, acetone, acetonitrile and ethanol.

Electronic absorption spectra and structure of hydroxycoumarin derivatives and their ionized forms

1997 ◽  
Vol 75 (4) ◽  
pp. 365-376 ◽  
Author(s):  
Valery F. Traven ◽  
Larisa I. Vorobjeva ◽  
Tatjana A. Chibisova ◽  
Edward Andrew Carberry ◽  
Noelle Jean Beyer
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Bathochromic Shift ◽  
Hydroxyl Group ◽  
Absorption Bands ◽  
Pyrone Ring ◽  
Tautomeric Forms ◽  
Wavelength Absorption ◽  
Carbonyl Function

Electronic absorption spectra of 18 hydroxycoumarin derivatives and their ionized forms have been studied. Close agreement between experimental and the PPP CI calculated electron absorption band energies has been found in most cases. Strong polarization of the carbonyl function of the pyrone ring in the 7-hydroxycoumarin derivatives, H-bonding between the hydroxyl group and neighboring substituent in the ortho-substituted hydroxycoumarins, as well as their tautomeric transformations, have been suggested in the discussion of the electronic absorption spectra of the hydroxycoumarin derivatives. In accord also with calculational results, ionization of the hydroxyl function leads to a bathochromic shift of the longest-wavelength absorption bands in the spectra of 7-hydroxycoumarin derivatives. The ionization has no effect on the electronic absorption of the 4-hydroxycoumarin derivatives. Relative stabilities of the tautomeric forms of hydroxycoumarin derivatives and their ionized forms have also been compared by MNDO calculations. Keywords: hydroxycoumarins, intramolecular H-bonding, ionization, electronic absorption spectra, keto–enol tautomerism.

Stereochemistry of [carbonato-bis((S)-prolinato)]cobaltate(III) anion

1984 ◽  
Vol 49 (3) ◽  
pp. 680-683 ◽  
Author(s):  
Bohumil Hájek ◽  
Dagmar Sýkorová ◽  
Jiří Chyba
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Cd Spectra

The λ-C1-cis(N), δ-C1-cis(N), λ-C2-cis(N) and δ-C2-cis(N) isomers of the complex K[Co((S)-Pro)2CO3] were chromatographically separated and characterized by their electronic absorption spectra and CD spectra.

Photocolouration of 2,4,4,6-Tetraaryl-4H-pyrans and Their Heteroanalogues: Importance of Hypervalent Photoisomers

1995 ◽  
Vol 60 (10) ◽  
pp. 1621-1633 ◽  
Author(s):  
Stanislav Böhm ◽  
Mojmír Adamec ◽  
Stanislav Nešpůrek ◽  
Josef Kuthan
Keyword(s):  
Reaction Kinetics ◽  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Theoretical Data ◽  
Order Reaction ◽  
Bleaching Process ◽  
First Order ◽  
Photodegradation Products ◽  
Hypervalent Molecules

Molecular geometries of 2,4,4,6-tetraphenyl-4H-pyran (Ia), 4,4-(biphenyl-2,2e-diyl)-2,6-diphenyl-4H-pyran (Ib) and their heterocyclic isomers II-V were optimized by the PM3 method and used for the calculation of electronic absorption spectra by the CNDO/S-CI procedure. Comparison of the theoretical data with experimental UV-VIS absorption spectra made possible to select hypervalent molecules IIIa, IIIb, IVa and IVb being responsible for the photocolouration of 4H-pyrans Ia, Ib, while compounds Va, Vb, VI and VII come into account as possible photodegradation products. The bleaching process of the UV illuminated compound Ia is analyzed in terms of dispersive first-order reaction kinetics.

Niobocene Dichloride and Niobocene Diiodide: Electronic Absorption Spectra and Electron Spin Resonance

1998 ◽  
Vol 63 (5) ◽  
pp. 628-635 ◽  
Author(s):  
Jana Holubová ◽  
Zdeněk Černošek ◽  
Ivan Pavlík
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Point Group ◽  
Esr Spectra ◽  
Ligand Field ◽  
Orbital Interaction ◽  
Symmetry Point Group ◽  
Spin Orbital ◽  
Halide Ligands

The effect of the halide ligand on the bonding of niobium in niobocene dichloride and niobocene diiodide was investigated. The electronic absorption spectra of the two compounds in the range of d-d transitions were resolved into four bands corresponding to transitions of the d1 electron between five frontier orbitals in a molecule of symmetry point group C2v. The energies of the frontier molecular orbitals were determined relatively to the energy of the orbitals in the spherically symmetric ligand field formed by the appropriate halide ligands. The effect of the halide ligands on the spin-orbital interaction of the HOMO orbital is discussed qualitatively on the basis the ESR spectra.

π* ← π systems in the electronic absorption spectra of some trisubstituted benzenes

1992 ◽  
Vol 48 (7) ◽  
pp. 983-991 ◽  
Author(s):  
M.K. Aralakkanavar ◽  
N.R. Katti ◽  
P.R. Jeergal ◽  
G.B. Kalkoti ◽  
Rekha Rao ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra
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