Investigation on catalytic systems containing nickel supported on silica and bonded with organic ligands and complexed by lewis acids

The catalytic properties of the

(n = 0–3) system, resulting from the reaction of (C₃H₅)₂Ni with hydroxide groups of silica gel and complexation with a Lewis acid, MeAlCl₂, have been studied in the oligomerization of propylene. It has been ascertained that when n > 3 the excess of MeAlCl₂ is carried out from the catalyst bed by the products. The yield of the product is influenced by the rate of propylene flow and the composition of the catalyst. The yield of products increases with the rise in the propylene flow rate. The highest yield was obtained for n = 1 and the flow of propylene = 360 ml/min g. The elimination by the olefin of the allyl group from the complex in the initial stages of oligomerization was ascertained. This testifies to the formation of new forms of the surface nickel complex that should contain catalytically active NiH or NiR bonds. The EPR studies determined the valence of nickel in this system (n = 1) to be +2 and thus made it possible to propose its structure.     

Shell structure studies in the titanium region with 52 mev deuterons

The (d,³He)-reactions on the target nuclei^48,50Ti and⁵¹V have been studied with 52 MeV deuterons. The data were analyzed by means of the DWBA which is shown to be applicable at this energy. All our results agree well with the assumption of pure (f _7/2)ⁿ proton configurations for these nuclei. The inelastic scattering of 52 MeV deuterons from the lowest 2⁺ state in⁴⁸Ti has been described in terms of the collective model as well as of the microscopic shell model. Good fits to the measured angular distributions have been obtained with reasonable values for the deformation parameters and the basic nucleon-nucleon interaction.     

Dominance of α decay from the isoscalar giant quadrupole resonance in 16O

The charged particle (c) decay of the isoscalar giant quadrupole resonance in a ¹⁶O has been studied in a ¹⁶O(α,α'c) coincidence experiment at E_α=155 MeV. The J=2 character of this resonance was established by angular correaltion measurements. Its dominant decay proceeds through the α₁ channel which contains about 40% of the E2 energy weighted sum rule. This explains difficulties of capture reactions to locate the GQR.     

A Comparative Study of the Determination of Ferrofluid Particle Size by Means of Rotational Brownian Motion and Translational Brownian Motion

Two methods, the Toroidal Technique and the Forced Rayleigh Scattering (FRS) method, were used in the determination of the size of magnetic particles and their aggregates in magnetic fluids. The toroidal technique was used in the determination of the complex, frequency dependent magnetic susceptibility, x(w)=x'(w) - ix"(w) of magnetic fluids consisting of two colloidal suspensions of cobalt ferrite in hexadecene and a colloidal suspension of magnetite in isopar m with corresponding saturation magnetisation of 45.5 mT, 20 mT and 90 mT, respectively. Plots of the susceptibility components against frequency f over the range 10 Hz to 1 MHz, are shown to have approximate Debye-type profiles with the presence of relaxation components being indicated by the frequency, f _max, of the maximum of the loss-peak in the x"(w) profiles. The FRS method (the interference of two intense laser beams in the thin film of magnetic fluid) was used to create the periodical structure of needle like clusters of magnetic particles. This creation is caused by a thermodiffusion effect known as the Soret effect. The obtained structures are indicative of as a self diffraction effect of the used primary laser beams. The relaxation phenomena arising from the switching off of the laser interference field is discussed in terms of a spectrum of relaxation times. This spectrum is proportional to the hydrodynamic particle size distribution. Corresponding calculations of particle hydrodynamic radius obtained by both mentioned methods indicate the presence of aggregates of magnetic particles.     

From a 2,1-Benzazaarsole to Elusive 1-Arsanaphthalenes in One Step

The 2,1-benzazaarsole ( 1 ) showed a diene-like reactivity towards selected alkynes RC≡CR (R=CO₂Me, C₅F₄N) thus forming 1-arsa-1,4-dihydro-iminonaphthalenes 2 a and 3 a as hardly isolable intermediates, that underwent facile CH→NH proton migration leading to before elusive substituted 1-arsanaphthalenes 2 b and 3 b that could be completely structurally characterized.     

Dimers of N‐Heterocyclic Carbene Copper,Silver, and Gold Halides: Probing Metallophilic Interactions through Electron Density Based Concepts

Homobimetallic metallophilic interactions between copper, silver, and gold‐based [(NHC)MX]‐type complexes (NHC=N‐heterocyclic carbene, i.e, 1,3,4‐trimethyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene; X=F, Cl, Br, I) were investigated by means of ab initio interaction energies, Ziegler–Rauk‐type energy‐decomposition analysis, the natural orbital for chemical valence (NOCV) framework, and the noncovalent interaction (NCI) index. It was found that the dimers of these complexes predominantly adopt a head‐to‐tail arrangement with typical M ??? M distance of 3.04–3.64 Å, in good agreement with the experimental X‐ray structure determined for [{(NHC)AuCl}₂], which has an Au ??? Au distance of 3.33 Å. The interaction energies between silver‐ and gold‐based monomers are calculated to be about ?25 kcal mol^?1, whereas that for the Cu congener is significantly lower (?19.7 kcal mol^?1). With the inclusion of thermal and solvent contributions, both of which are destabilizing, by about 15 and 8 kcal mol^?1, respectively, an equilibrium process is predicted for the formation of dimer complexes. Energy‐decomposition analysis revealed a dominant electrostatic contribution to the interaction energy, besides significantly stabilizing dispersion and orbital interactions. This electrostatic contribution is rationalized by NHC(δ⁺) ??? halogen(δ^?) interactions between monomers, as demonstrated by electrostatic potentials and derived charges. The dominant NOCV orbital indicates weakening of the π backdonation in the monomers on dimer formation, whereas the second most dominant NOCV represents an electron‐density deformation according to the formation of a very weak M ??? M bond. One of the characteristic signals found in the reduced density gradient versus electron density diagram corresponds to the noncovalent interactions between the metal centers of the monomers in the NCI plots, which is the manifestation of metallophilic interaction.     

Preparation of 5-Substituted 1H-Tetrazoles Catalyzed by Scandium Triflate in Water

Several 5-substituted 1H-tetrazoles were prepared in water or isopropanol/water mixtures using microwave heating. Good yields were obtained for the [2 + 3] cycloaddition of sodium azide with aryl nitriles, aliphatic nitriles, and vinyl nitriles when catalyzed by scandium triflate. The reactions were typically heated for 1 h at 160 °C in a 3:1 isopropanol/water mixture to obtain the best yields.     

A novel compact nomenclature of the condensed benzenoid hydrocarbons

Rules of a simplified nomenclature are formulated for condensed benzenoid hydrocarbons. They refer to all the hydrocarbons which could be treated as plane. In naming the hydrocarbon use is made of the numerator determining the number of rings and of the numeric code describing their immediate positional relationship. The proposed nomenclature enables quick and simple assignment of the name to the hydrocarbon and also provides a useful method for deriving the hydrocarbon structural formula from its name.     

Reaction of nitroalkane in the presence of solid bases prepared under various conditions

Alumina for chromatography (acidic, basic and neutral), magnesia and sodium-doped magnesia calcined at 350, 450, 550, 650 and 750^oC for 4 h were used as solid bases to catalyze the synthesis of 1-nitro-2-butanol from nitromethane and propionaldehyde (Henry reaction). This revised version was published online in June 2006 with corrections to the Cover Date.