Chemistry of polybutadiene—iron carbonyl systems

The treatment of polybutadienes with iron carbonyls results in formation of polymers containing tricarbonyl(conjugated diene)iron units [C₈H₁₂Fe(CO)₃] and also results in geometrical isomerization of free double bonds. Heating of the iron carbonyl-containing polymers gives ferromagnetic products with enhanced thermal stability. The incorporation of iron carbonyl groups into the polymer is favored by basic solvents and high temperatures, the geometrical isomerization by acidic solvents and low temperatures. Steric factors are powerful in determining the rate of isomerization.     

Nitroxydes-LXVIII : Synthese et etude cinetique de la decomposition du t-butyl isopropyl nitroxyde. Effet isotopique

Decomposition of t-butyl isopropyl nitroxide and its β²H-labelled homologue has been examined by UV and EPR. The bimolecular reaction does not show reversible formation of a dimer, but exhibits an isotope effect (k_H/k_d)_30°C?9 which shows that the rupture of the CH bond is involved in the slow step of the decomposition. The β proton coupling constant, determined by NMR, is +1.84 G.     

Structure électronique et spectres de resonance paramagnétique électronique des radicaux vinyle et cyclopropyle

Résumé Une méthode de calcul dérivant des théories de champ self-consistant est utilisé pour l'étude des radicaux vinyle et cyclopropyle. L'énergie électronique et les écarts hyperfins dûs aux hydrogènes et au ¹³C ont été évalués en fonction de la géométrie du carbone radicalaire. L'angle C=-H du radical vinyle a été trouvé de l'ordre de 150°. Il est montré que les radicaux vinyle et cyclopropyle ont une structure électronique similaire qui ne peut être totalement expliquée ni par un modèle ni par un modèle classique, chaque radical présentant à la fois les deux caractères.

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A method of calculation derived from self-consistent field theories is used for a study of vinyl and cyclopropyl radicals. Electronic energy, hydrogens and ¹³C hyperfine splittings are evaluated as a function of the carbon geometry. The C=-H bond angle is found to be about 150°. It is shown that vinyl and cyclopropyl radicals have a similar electronic structure which cannot be completely interpreted neither by a classical model nor by a one, each radical presenting both and character.

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Zusammenfassung Nach einer auf dem SCF-Verfahren basierenden Methode werden Elektronenenergie, H- und ¹³C-Hyperfeinaufspaltung in Vinyl- und Cyclopropylradikalen in Abhängigkeit vom Bindungswinkel am berechnet, der sich im ersten Fall zu 150° ergibt. Es zeigt sich, daß die Elektronenstruktur der beiden behandelten Radikale ähnlich ist und daß sie weder durch ein reines - noch ein reines -Modell zu beschreiben ist.

     

Activation thermodynamic parameters of binary mixtures of propionic acid ando-substituted anilines

Variations of densities and viscosities with temperature and composition are reported for binary liquid mixtures containing propionic acid+aniline (I),+o-toluidine (II),+o-anisidine (III), and+o-chloroaniline (IV). Entropies S _m and enthalpies H _m of activation as functions of the composition of the mixtures, as well as free energies of activation G _m at 10, 20, 30, 40, and 50°C and different compositions were calculated by means of Eyring's equation. The formation of activated complexes between the components of these binary mixtures is postulated and claimed to result from acid-base and hydrogen bonding exchange interactions.     

Freeze–Thaw-Promoted Fabrication of Clean and Hierarchically Structured Noble-Metal Aerogels for Electrocatalysis and Photoelectrocatalysis

Noble-metal aerogels (NMAs) have drawn increasing attention because of their self-supported conductive networks, high surface areas, and numerous optically/catalytically active sites, enabling their impressive performance in diverse fields. However, the fabrication methods suffer from tedious procedures, long preparation times, unavoidable impurities, and uncontrolled multiscale structures, discouraging their developments. By utilizing the self-healing properties of noble-metal aggregates, the freezing-promoted salting-out behavior, and the ice-templating effect, a freeze–thaw method is crafted that is capable of preparing various hierarchically structured noble-metal gels within one day without extra additives. In light of their cleanliness, the multi-scale structures, and combined catalytic/optical properties, the electrocatalytic and photoelectrocatalytic performance of NMAs are demonstrated, which surpasses that of commercial noble-metal catalysts.