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.

Photocolouration of 2,4,4,6-Tetraaryl-4H-thiopyrans: A Semiempirical Quantum Chemical Study

1994 ◽  
Vol 59 (5) ◽  
pp. 1115-1125 ◽  
Author(s):  
Stanislav Böhm ◽  
Pavel Šebek ◽  
Stanislav Nešpůrek ◽  
Josef Kuthan
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Quantum Chemical ◽  
Electronic Absorption Spectra ◽  
Quantum Chemical Study ◽  
Theoretical Data ◽  
Chemical Study ◽  
Pm3 Method ◽  
Uv Illumination

Molecular geometries of 4H-thiopyrans Ia, Ib and their possible photoisomers IVa - VIIa and IVb - VIIb were optimized by the AM1 and 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 it possible to postulate two probable mechanisms of the photocolouration of Ia, Ib caused by sunlight or UV-illumination.

Reactions of pyrazine radical anions in solution. I. Study of the kinetics of the dimerization of pyrazine radical anions

1971 ◽  
Vol 24 (11) ◽  
pp. 2287 ◽  
Author(s):  
RS Hay ◽  
PJ Pomery
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Rate Constants ◽  
Electronic Absorption Spectra ◽  
Radical Anions ◽  
Light Reaction ◽  
First Order ◽  
Kinetics Of Reaction ◽  
Kinetics Of ◽  
Metallic Potassium

The radical anions of pyrazine (pz-.) have been prepared at 294'K by reducing pyrazine (pz) with metallic potassium in 1,2-dimethoxyethane (dme). The resulting reactions of the radical anions are postulat'ed as being described by the equations: The e.s.r, and electronic absorption spectra of all pertinent species were recorded and examined. The kinetics of reaction (1) have been investigated in the dark as well as in light and values of the rate constants have been determined. I n light, reaction (1) did not conform strictly to second-order kinetics and this may be explained by an interaction of pyrazine with dme. The dimer dianion species (-pz-pz-, 2K7) was found to be stable in the dark but decayed slowly in light. This decay was found to exhibit first-order kmetics.

Electronic absorption spectra and dipole moments of diazafluoren-9-ones studied by the MIM, PPP, and CNDO/2 methods

1976 ◽  
Vol 54 (12) ◽  
pp. 1870-1874 ◽  
Author(s):  
Concetta Gandolfo ◽  
Giuseppe Buemi ◽  
Domenico Grasso ◽  
Salvatore Fasone
Keyword(s):  
Absorption Spectra ◽  
Satisfactory Agreement ◽  
Electronic Absorption ◽  
Electronic Spectra ◽  
Benzene Solution ◽  
Electronic Absorption Spectra ◽  
Dipole Moments ◽  
Theoretical Data ◽  
Uv Spectra

The electronic spectra of three diazafluoren-9-one isomers have been measured in cyclohexane solution and the results compared with those of 'molecules in molecules'(MIM) and PPP calculations. A satisfactory agreement between experimental and theoretical data has been found, and five π → π* transitions can be assigned to their uv spectra. For two compounds dipole moments in benzene solution have been measured and results are compared with theoretical values obtained by MIM and CNDO/2 calculations.

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.

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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