Dialkyl Peroxides Decomposition in the Presence of Quaternary Ammonium Halides

Decomposition of dicumyl peroxide and cumyl tert-butyl peroxide was studied in the presence of tetraethylammonium halides in acetonitrile, dimethylformamide, 2-propanol, and acetic acid. The tetraethylammonium halides accelerate the decomposition of dialkyl peroxides in 2-propanol and acetic acid, but do not affect the reaction velocity in dimethylformamide and acetonitrile. The decomposition products character depends on the solvent nature.     

Raman scattering of light by optical phonons in Si-Ge-Si structures with quantum dots

Raman scattering of light by optical phonons in Si-Ge-Si structures with pseudomorphic germanium quantum dots has been investigated. Resonance amplification of the scattering intensity on E ₀ (Γ₇−Γ₈) transitions has been observed. It is shown that as a result of the formation of the layer of germanium quantum dots, the resonance energy is ∼0.3 eV higher than in the two-dimensional case. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 203–207 (10 August 1996)     

Effect of an electron beam on CaF<Subscript>2</Subscript> and BaF<Subscript>2</Subscript> epitaxial layers on Si

Atomically smooth CaF₂ and BaF₂ layers have been sequentially grown on Si(111) substrates by molecular beam epitaxy. Pore macrodefects have been revealed at the points of the action of an electron beam from a diffractometer when analyzing the crystal structure of the surface during the growth with the subsequent observation using atomic force microscopy. The formation of these macrodefects is associated with the decomposition of fluorides by high-energy electrons, which is accompanied by the desorption of fluorine and the drift current of positive ions from the electron charge drains.     

Inorganic Anionic Oxygen-Containing α-Nucleophiles-Effective Acyl Group Acceptors: Hydroxylamine Ranks First among the α-Nucleophile Series

Comparative analysis of the nucleophilicity of inorganic oxygen-containing -nucleophiles (hydroxylamine and ClO^-, BrO^--, HOO^--, NH₂O^-, and F^- ions) covering the pK _a range from -2 to 13.81 toward 4-nitrophenyl esters (4-nitrophenyl acetate, 4-nitrophenyl p-toluenesulfonate, diethyl 4-nitrophenyl phosphate, ethyl 4-nitrophenyl ethylphosphonate, and 4-nitrophenyl dimethylcarbamate) in water at 25°C (ionic strength 1.0, KCl) was performed in terms of the extrathermodynamic Brönsted relation. It was found for the first time that hydroxylamine anion ranks first among the series of -nucleophiles. It is more reactive than HOO^- ion with respect to 4-nitrophenyl acetate (by a factor of 8), 4-nitrophenyl p-toluenesulfonate (by a factor of 4) and 4-nitrophenyl dimethylcarbamate (by a factor of 10). The nucleophilicities of HOO^- and NH₂O^- ions toward diethyl 4-nitrophenyl phosphate and ethyl 4-nitrophenyl ethylphosphonate are comparable. Taking into account that neutral hydroxylamine exhibits an anomalously high reactivity, as compared to not only common organic but also inorganic -nucleophiles, it may be regarded as a unique -nucleophile. Both neutral hydroxylamine and its anion as O-nucleophiles ensure high rates of acyl group transfer throughout a wide range of pH.     

Synthesis and Recyclization of Methylenebisflavonoids Based on Heterocyclic Analogs of Umbelliferone and Formononetin

Chemistry of Natural Compounds - The methylenebisflavonoids 7-hydroxy-3-hetaryl-8-(4-oxo-4H-3-chromenylmethyl)-4H-4-chromenones and...     

Raman E 1, E 1+Δ1 resonance in unstrained germanium quantum dots

Raman scattering by optical phonons in unstrained Ge quantum dots obtained in GaAs/ZnSe/Ge/ZnSe structures was studied using molecular beam epitaxy. A shift in the E ₁, E ₁+Δ1 resonance energy due to the quantization of the spectrum of electron and hole states in quantum dots was observed. The properties observed were explained with the use of a simplest model of localization with allowance for the spectrum of Ge electron states.     

Effect of Gadolinium Additives on the Active Phase Morphology and Physicochemical and Catalytic Properties of MoVSbNbGdOx/SiO2 Catalysts in the Oxidative Dehydrogenation of Ethane to Ethylene

Kinetics and Catalysis - The effect of gadolinium additives on the morphology, phase composition, and catalytic properties of MoVSbNbGdOx/SiO2 catalysts in the oxidative dehydrogenation of ethane...