Etude du Comportement Photochimique de quelques Diaryl-1,3-triazènes

Study of the Photochemical Behaviour of Some Diaryl-1,3-triazenes The photolysis of Diaryl-1,3-triazenes gives products whose structures are consistent with a cage recombination process of homolytically formed radicals and subsequent abstraction of hydrogen from the solvent molecules by arylamino radicals. In aromatic solvents, a free-radical chain process leads to the formation of products resulting from the homolytic substitution on the solvent. Quenching experiments show that singlet and triplet excited states are reactive but that intersystem crossing efficiency is low.     

Symmetry components analysis of nuclear spin–spin coupling constants

Molecular symmetry properties are used to define “normal” spin–spin coupling constants corresponding to some irreducible representations of the symmetry point group of the molecule. The relationship between these normal coupling constants and the measured ones is established in closed form for the most common cases. The Ramsey perturbation formula is analysed into symmetry components by means of the Winger–Eckart theorem. Both contributions predicted by the molecular-orbital method, i. e. direct coupling via σ electrons and indirect coupling via σ–π interaction are studied. Numerical calculations for the coupling constants of ethane, ethylene and acetylene were carried out without the mean excitation energy approximation by using SCF ? MO wave functions; overlap between atomic orbitals is systematically taken into account by calculating coupling constants. Theoretical and experimental results are compared in terms of symmetry components.     

NMR proofs of the involvement of an allenyl-naphthol as a key-intermediate in the photochromic process of [3H]-naphthopyrans

The NMR characterization of an intermediate, proved to be involved in the photochromic process of fluoro-substituted-3,3-diphenyl-3H-naphtho[2,1-b]pyrans is reported. An o-allenyl-naphthol structure was deduced and a plausible reaction mechanism was proposed.     

Degradations photothermiques de polyethylenes reticules. II.—Action photocatalytique d'oxydes metalliques

The chemical modifications of a cross-linked polyethylene sample submitted to photocatalyzed oxidation have been investigated by infra-red spectrophotometry; the spectral changes are compared with those observed in thermal and photothermal oxidation. Zinc oxides and both titanium oxides (anatase and rutile) behaved similarly as photocatalysts. Under excitation by monochromatic light, initial quantum yields of formation of aliphatic ketones have been determined; their variations with macroscopic parameters (excitation wavelength, light intensity, per cent of the photocatalytic oxide) have been studied. Activation energies of the photocatalytic conversion of polyethylene into ketones have been measured under polychromatic light. Finally, it is shown that the simultaneous addition of a photocatalytic oxide and a quinolinic antioxidant is efficient against the oxidative photodegradation of polyethylene.     

Structure électronique et stabilité thermique d'heterocycles appartenant à la serie de l'imidazole et du thiazole

Résumé La structure électronique de l'imidazole, du benzimidazole, du thiazole et du benzothiazole a été calculée par une méthode de champ self-consistant simplifiée tenant compte des électrons et . L'énergie d'arrachement d'un atome d'hydrogène fixé sur le noyau hétérocyclique a été évaluée de faÇon approximative, en vue d'interpréter la variation de stabilité observée dans les expériences de pyrolyse.

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The electronic structure of imidazole, benzimidazole, thiazole and benzothiazole has been calculated by a simplified LCAO-SCF method taking into account and electrons. Breacking energy for an hydrogen atom bounded to the heterocyclic ring is estimated by an approximated way and used for explaining changes of stability observed in pyrolysis experiments.

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Zusammenfassung Die Elektronenstruktur von Imidazol, Benzimidazol, Thiazol und Benzthiazol wurde mittels eines vereinfachten LCAO-SCF-Verfahrens unter Einschlu\ von - und -Elektronen berechnet. Dann wurde die Trennungsenergie für ein am Heteroring gebundenes H-Atom abgeschÄtzt und zur Interpretation der relativen StabilitÄt, wie sie bei Pyrolysen beobachtet wird, verwendet.

     

The Pathmox approach for PLS path modeling segmentation

Modeling has often failed to meet expectations, mostly because of the difficulty of comprehending relationships within phenomena and expressing them in mathematical models. Reality is frequently too complex to be reflected in a single model. This is often the case of marketing research, where variables relating to socioeconomics or psychographics constitute potential sources of heterogeneity. In such cases, the assumption of ‘one model fits all’ is unrealistic and may lead to inaccurate decisions. Thus, heterogeneity is a major issue in modeling. Once a model has been fitted to a complete data set that fulfills all validation criteria, it is difficult to establish whether it is valid for the whole population or it is merely an average artifact from several sub‐populations. The purpose of this paper is to present the Pathmox approach to deal with heterogeneity in partial least squares path modeling. The idea behind Pathmox is to build a tree of path models that have look‐alike structure as a binary decision tree, with different models for each of its nodes. The split criterion consists of an F statistic comparing two structural models. In order to ensure the suitability of the split criterion, a simulation study was conducted. Finally, we have applied Pathmox to a survey that measured Satisfaction among Spanish mobile phone operators. Results suggest that the Pathmox approach performs adequately in detecting partial least squares path modeling heterogeneity. Copyright © 2016 John Wiley & Sons, Ltd.     

From the Superatom Model to a Diverse Array of Super‐Elements: A Systematic Study of Dopant Influence on the Electronic Structure of Thiolate‐Protected Gold Clusters

The electronic properties of doped thiolate‐protected gold clusters are often referred to as tunable, but their study to date, conducted at different levels of theory, does not allow a systematic evaluation of this claim. Here, using density functional theory, the applicability of the superatomic model to these clusters is critically evaluated, and related to the degree of structural distortion and electronic inhomogeneity in the differently doped clusters, with dopant atoms Pd, Pt, Cu, and Ag. The effect of electron number is systematically evaluated by varying the charge on the overall cluster, and the nominal number of delocalized electrons, employed in the superatomic model, is compared to the numbers obtained from Bader analysis of individual atomic charges. We find that the superatomic model is highly applicable to all of these clusters, and is able to predict and explain the changing electronic structure as a function of charge. However, significant perturbations of the model arise due to doping, due to distortions of the core structure of the Au₁₃[RS(AuSR)₂]₆^? cluster. In addition, analysis of the electronic structure indicates that the superatomic character is distributed further across the ligand shell in the case of the doped clusters, which may have implications for the self‐assembly of these clusters into materials. The prediction of appropriate clusters for such superatomic solids relies critically on such quantitative analysis of the tunability of the electronic structure.     

Electronic structure, chemical bonding, and geometry of pure and Sr-doped CaCO3

The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures.     

Sur la Conjecture de Fermat

All the letters represent relative integers, except and and i = e₁e₂ in R(2, 0) oder e₁ in R(1, 0). We study the Fermat’s equation

Catalytic Potential of Post-Transition Metal Doped Graphene-Based Single-Atom Catalysts for the CO2 Electroreduction Reaction

Catalysts are required to ensure electrochemical reduction of CO₂ to fuels proceeds at industrially acceptable rates and yields. As such, highly active and selective catalysts must be developed. Herein, a density functional theory study of p-block element and noble metal doped graphene-based single-atom catalysts in two defect sites for the electrochemical reduction of CO₂ to CO and HCOOH is systematically undertaken. It is found that on all of the systems considered, the thermodynamic product is HCOOH. Pb/C₃, Pb/N₄ and Sn/C₃ are identified as having the lowest overpotential for HCOOH production while Al/C₃, Al/N₄, Au/C₃ and Ga/C₃ are identified as having the potential to form higher order products due to the strength of binding of adsorbed HCOOH.