Evidences on the intermediacy of furoxan in the flash vacuum thermolysis of some 4-Nitroisoxazoles

The kinetic measurements in the Flash Vacuum Thermolysis (FVT) of 3,5-Dimethyl- and 5-Methyl- 4-Nitroisoxazole confirm the already suggested intermediacy of the isomer 2H-Azirine in the formation of 1- Cyano-1-Nitroacetone. Moreover, theoretical calculations of the stabilization energy (E_s), at the transition state, using second order perturbation suggest that this azirine is formed through the isomer furoxan rather than directly from the starting isoxazole.     

Calculations of spin-spin coupling constants with the self-consistent polarization propagator approximation in non-singlet unstable wavefunctions

Nuclear spin-spin coupling constants are calculated with the self-consistent polarization propagator approximation method starting from a semi-empirical non-singlet unstable wavefunction. Effects on α and π transmitted components are separately analysed. Resultss show that this approximation is an adequate framework for the Fermi contact term when the corresponding HF state presents a non-singlet instability.     

Copper(II) complexes of 4-chloro,3-methyl,5-phenylisoxazole

4-chloro,3-methyl,5-phenylisoxazole copper(II) complexes of the type Cu(L)X₂(X = Cl, Br, NO₃) and Cu(L)₂(ClO₄)₂ have been prepared and studied by the IR, electronic, paramagnetic resonance spectroscopy and molar conductivity values. The ligand acts as monodentate N-bonded except to the nitrate derivative where this behaves as bridging bidentate. The halide complexes are tetrahedral, while the nitrate and perchlorate derivatives are square planar.     

Structural and spectroscopic properties ofμ-catena-iodomonoiodo-N-ethylimidazolemercury(II)

The crystal and molecular structure of the title compound is reported. The crystals are monoclinic,P2₁/c,a=9.578 (1),b=15.339 (2),c=7.674(1) Å,=109.61(1)°. The structure was solved by Patterson and Fourier methods, and refined by full-matrix least squares toR=0.0542,R _w =0.0575 for 645 unique reflections. Coordination around the mercury is intermediate between tetrahedral and trigonal pyramidal with two terminal and two bridging bonds. Vibrational spectra were also redetermined and discussed.     

Union of chiral and heavy quark symmetries

We describe the chiral symmetric couplings of pions to heavy mesons (B or D), valid in the portion of phase space where the pions have low momentum. In order to include consistently all low energy excitations, the vector mesons (B^* or D^*) must appear explicitly in the effective lagrangian. The result is then invariant under both the chiral and heavy quark symmetries. We include matrix elements relevant for various weak decays.     

1,1-Diamino-2-nitroethylenes as excellent hydrogen bond donor organocatalysts in the Michael addition of carbon-based nucleophiles to β-nitrostyrenes

A new class of hydrogen bond donor catalysts based on the 1,1-diamino-2-nitroethylene scaffold has been introduced for the activation of trans-β-nitrostyrenes toward reactions with a range of carbon-based nucleophiles, affording the corresponding adducts in excellent yields. Importantly, this new set of organocatalysts is easily prepared from commercially available starting materials in mild reaction conditions.     

Development of a fast capillary electrophoresis method to determine inorganic cations in biodiesel samples

The aim of this study was to develop a fast capillary electrophoresis method for the determination of inorganic cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) in biodiesel samples, using barium (Ba²⁺) as the internal standard. The running electrolyte was optimized through effective mobility curves in order to select the co-ion and Peakmaster software was used to determine electromigration dispersion and buffer capacity. The optimum background electrolyte was composed of 10 mmol L⁻¹ imidazole and 40 mmol L⁻¹ of acetic acid. Separation was conducted in a fused-silica capillary (32 cm total length and 23.5 cm effective length, 50 μm I.D.), with indirect UV detection at 214 nm. The migration time was only 36 s. In order to obtain the optimized conditions for extraction, a fractional factorial experimental design was used. The variables investigated were biodiesel mass, pH, extractant volume, agitation and sonication time. The optimum conditions were: biodiesel mass of 200 mg, extractant volume of 200 μL and agitation of 20 min. The method is characterized by good linearity in the concentration range of 0.5-20 mg kg⁻¹ (r > 0.999), limit of detection was equal to 0.3 mg kg⁻¹, inter-day precision was equal to 1.88% and recovery in the range of 88.0-120%. The developed method was successfully applied to the determination of cations in biodiesel samples.     

Partial isometries in semi-Hilbertian spaces

In this work, the concepts of isometry, unitary and partial isometry on a Hilbert space are generalized when an additional semi-inner product is considered. These new concepts are described by means of oblique projections.     

The equal award principle in problems with constraints and claims

In this paper we study how, under the equal award principle, to distribute a resource among different agents with a claim on it, when there are some constraints in the problem. Some properties of the rule are given as well as an axiomatic characterisation.