ESR and calculations on electronic structure of phenalenyl and phenalenyl derivative radicals

Calculations on electronic structure of the perinaphthenyl radical and phenalenyl derivative radicals responsible for the composition of the ESR spectrum of marine diesel under heating were performed to obtain support for the experimental ESR results. The parameters calculated were the hyperfine coupling constants (A), which were then used for comparison with the experimental data. The energy‐minimized structures were obtained using the density functional theory method. In all cases, the symmetry system was taken into account in theoretical calculations. The differences between experimental and theoretical values were below 7% for nearest hydrogens in molecules, named hyperfine coupling constant A (first neighbors) and 18% for farthest hydrogens atoms named hyperfine coupling constants A′ (second neighbors), for all structures analyzed. Copyright © 2014 John Wiley & Sons, Ltd.     

Calculations on the electronic spectra of anilino,phenoxyl and benzyl radicals

The electronic spectra of benzyl, anilino and phenoxyl have been calculated, using two well known SCF-MO methods. Good agreement is found with experiment in all instances. However, the calculations still cannot explain the red shift produced by the addition of an extra electron to benzyl.

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Zesummenfassung Die Elektronenspektren des Benzyl-, Anilino- und Phenoxylradikals sind mit Hilfe zweier wohlbekannter SCF-MO-Methoden berechnet worden. Die Übereinstimmung mit den Experimenten ist überall gut. Die Rechnungen können jedoch nicht die Rotverschiebung erklären, die beim Hinzufügen eines Elektrons zum Benzylradikal erzeugt wird.

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Resume On calcule les spectres électroniques des radicaux benzyle, anilino et phénoxyle par deux méthodes SCF-MO bien connues. L'accord avec l'expérience est bon partout. Cependant, ces calculs n'expliquent pas l'effet bathocrome de l'addition d'un électron au benzyle.

     

Electronic structure and nature of the bands in electronic absorption spectra of stable phenoxyl radicals of indophenoxyl and galvinoxyl

On the basis of results from quantum chemical calculations, made using the CNDO/S approximation method and taking into account configurational interaction, it has been shown that the first long-wave and subsequently more intense bands in the electronic absorption spectra of the phenoxyl radicals indophenoxyl and galvinoxyl are due to ^* electron transfers. The bands related to the p^* electron transfers of unshared p-electron pairs of oxygen and nitrogen atoms are located between them. It is suggested that displacement of the spectrum bands into the red region in transferring from the indophenoxyl to the galvinoxyl radical is caused by a reduction of the electron acceptor capacity of the bridging atom between the phenoxyl groups of the radical.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 737–740, November–December, 1987.     

Geometric and electronic structures of phenoxyl radicals hydrogen bonded to neutral and cationic partners

Two di-tert-butylphenols incorporating an N-methylbenzimidazole moiety in the ortho or para position have been synthesised ((Me)OH and (pMe)OH, respectively). Their X-ray structures evidence a hydrogen bond between the phenolic proton and the iminic nitrogen atom, whose nature is intra- and intermolecular, respectively. The present studies demonstrate that (Me)OH is readily oxidised by an intramolecular PET mechanism to form the hydrogen-bonded phenoxyl-N-methylbenzimidazolium system ((Me)OH)(.+) , whereas oxidation of (pMe)OH occurs by intermolecular PET, affording the neutral phenoxyl benzimidazole ((pMe)O)(.) system. The deprotonations of (Me)OH and (pMe)OH yield the corresponding phenolate species ((Me)O)(-) and ((pMe)O)(-), respectively, whilst that of the previously reported (H)OH (analogous to (Me)OH but lacking the N-methyl group) produces an unprecedented hydrogen-bonded phenol benzimidazolate species, as evidenced by its X-ray structure. The latter is believed to be in equilibrium in solution with its tautomeric phenolate form, as suggested by NMR, electrochemistry and DFT studies. The one-electron oxidations of the anions occur by a simple ET process affording phenoxyl radical species, whose electronic structure has been studied by HF-EPR spectroscopy and DFT calculations. In particular, analysis of the g(1) tensor shows the order 2.0079>2.0072>2.0069>2.0067 for ((Me)O)(.), ((H)O)(.), ((Me)OH)(.+) and ((H)OH)(.+), respectively. ((Me)O)(.) exhibits the largest g(1) tensor (2.0079), consistent with the absence of intramolecular hydrogen bond. The g(1) tensor of ((H)O)(.) is intermediate between those of ((Me)OH)(.+) and ((Me)O)(.) (g(1)=2.0072), indicating that the phenoxyl oxygen is hydrogen-bonded with a neutral benzimidazole partner.     

AB initio calculations of the electronic structure and doubling parameters of BS

Ab initio calculations have been performed to understand the influence of spin—orbit interaction upon the fine structure of the observed valence doublet states of the BS molecules: spin—orbit splittings, γ-type and Λ-type doublings. Configuration interaction is shown to be an essential feature in order to account for the observed data. Other properties of the electronic states (transition energies) have also been calculated.     

Persistent hydrogen-bonded and non-hydrogen-bonded phenoxyl radicals

The production of stable phenoxyl radicals is undoubtedly a synthetic chemical challenge. Yet it is a useful way to gain information on the properties of the biological tyrosyl radicals. Recently, several persistent phenoxyl radicals have been reported, but only limited synthetic variations could be achieved. Herein, we show that the amide-o-substituted phenoxyl radical (i.e. with a salicylamide backbone) can be synthesised in a stable manner, thereby permitting easy synthetic modifications to be made through the amide bond. To study the effect of H-bonding on the properties of the phenolate/phenoxyl radical redox couple, simple H-bonded and non-H-bonded o,p-tBu-protected salicylamidate compounds have been prepared. Their redox properties were examined by cyclic voltammetry and showed a fully reversible one-electron oxidation process to the corresponding phenoxyl radical species. Remarkably, the redox potential appears to be correlated, at least partially, with H-bond strength, as relatively large differences (ca. 300 mV) in the redox potential between H-bonded and non-H-bonded phenolate salts are observed. The corresponding phenoxyl radicals produced electrochemically are persistent at room temperature for at least an hour; their UV/Vis and EPR characterisation is consistent with that of phenoxyl radicals, which makes them excellent models of biological tyrosyl radicals. The analyses of the experimental data coupled with theoretical calculations indicate that both the deviation from planarity of the amide function and intramolecular H-bonding influence the oxidation potential of the phenolate. The latter H-bonding effect appears to be predominantly exerted on the phenolate and not (or only a little) on the phenoxyl radical. Thus, in these systems the H-bonding energy involved in the phenoxyl radical appears to be relatively small.     

Spatial and electronic structure and 35Cl NQR parameters of ethyl(trichlorogermyl) propionate according to Ab initio calculations

Two stable structures of ethyl(trichlorogermyl) propionate have been studied by RHF/6-31G(d) and MP2/6-31G(d) quantum-chemical caclulation with full geometry optimization. The structure with pentacoordinated Ge atom has been more stable than that with tetracoordinated Ge atom. Based on the computation results, the frequencies of ³⁵Cl nuclear quadrupole resonance of the studied compound with pentacoordinated Ge atom has been estimated, it has been in satisfactory agreement with the experimental data. Additionally, the calculations by means of the RHF/6-31G(d) method have been performed at various fixed Ge…O interatomic distances. When the Ge and O coordination centers get closer, both the positive charge on Ge and the negative charge on O increase. The electron density shifts from Ge atom to the axial Cl atom, and the electron density shifst from the carbonyl C atom to the carbonyl oxygen atom. The electron density charge trasfer from O to Ge does not occur.     

Wavelets for electronic structure calculations

Molecular electronic structure calculations have a multi‐scale character through the presence of a set of singularities corresponding to atomic nuclei, and thus there exists a potential to improve the efficiency of these calculations using fast wavelet transform techniques. We report on the development of a one dimensional prototype benchmark problem of sufficient complexity to capture the features of 3‐D problems that are being solved today in quantum electronics calculations. Theoretical estimates of decay across scales and spatial distribution of wavelet coefficients for the solutions of the 1‐D and 3‐D problems are derived and verified experimentally. Equivalence in a multi‐resolution context of the solutions of the 1‐D prototype and the 3‐D problem is established. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of solvation on the kinetic parameters of the reactions of phenoxyl radicals with phenols and semiquinone radicals with hydroquinones

Experimental rate constants of the reactions of semiquinone radicals with hydroquinones in chlorobenzene at ∼300 K are by almost an order of magnitude higher than the rate constants of the reactions of phenoxyl radicals with phenols, which are equivalent to the former ones by heat effects. To reveal differences in the rate constants of these groups of reactions, we performed quantum chemical calculations of the energy profiles of the reactions and dissociation energies by the B3LYP density functional theory using the GAMESS and GAUSSIAN-03 programs in the 6-31+G^* basis set. The solvation energies were calculated in all stationary points on the reaction coordinate by the method of polarized continuum model. In terms of the intersecting parabolas method, the reactions of semiquinone radicals with hydroquinones and phenoxyl radicals with phenols can be attributed to the same class of reactions only in the gas phase. In solvents this class of reactions is divided into two subclasses due to differences in solvation energies of the preliminary complexes and transition states of these reactions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1495–1501, September, 2006.     

Thermodynamic stability of the dimerization products of unsubstituted phenoxyl radicals according to data from quantum-chemical calculations determined by the MNDO method

The intermediate dimerization products of PhO^. of the C-O type are more stable than the C-C dimers, while the reverse relationship is. observed for the terminal products. The relative reactivity of the different centers in the phenoxyl radical correlates with the corresponding reorganization energies of the radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2267–2271, October, 1989.     

Polarographic study of some stable phenoxyl radicals

Conclusions A study was made of the polarographic reduction of phenoxyl radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2844–2845, December, 1971.