The chemistry of trityl isoselenocyanate revisited: A preparative and structural investigation

The reaction of trityl chloride with KSeCN gives trityl isoselenocyanate which was structurally characterised by X-ray diffraction. Trityl isoselenocyanate reacts with hydrazine to give trityl selenosemicarbazide and with primary amines to give selenourea derivatives. However, with secondary amines mixtures of selenoureas and substitution products are formed. Trityl selenosemicarbazide undergoes a condensation reaction with salicylaldehyde to give the corresponding trityl selenosemicarbazone. In the case of 2-pyridinecarboxaldehyde, the analogous selenosemicarbazone cannot be isolated, instead a small quantity of the diselenide was isolated from the reaction mixture. The compounds prepared here were fully characterised spectroscopically and several also by X-ray diffraction.     

Amélioration de la sensibilité de détection et de la qualité du radargramme d’un radar pénétrant GPR par une modulation micro-onde

The primary effect of the field continuously capted by aGpr is the production of a class which limits the contrast of the reflections on the targets. The target response becomes illegible sight the influence of certain disturbances which are due to the reflections caused by certain parasitic elements which are randomly distributed in the soil and the dispersion phenomenon. We present in this paper an approach based on a μ-wave modulation which allowed stage this problem. The technique suggested makes it possible to do a classification of capted signals. It will be shown that the frequency of modulation f_m must be higher than a cut-off frequency f_c which depends on the electric parameters of the ground. In a second part of this paper, we show how to improve quality of the radargram of a systemGpr by a simple convolution between the collected signal and a wavelet with a defined parameters.     

Effect of maleic anhydride and liquid natural rubber as compatibilizers on the mechanical properties and impact resistance of the NR‐NBR blend

The degree of compatibilization between natural rubber (NR) and acrylonitrile‐butadiene rubber (NBR) was investigated by two different methods. NBR was chemically modified with maleic anhydride in a screw twin mixer with and without reaction initiator, benzoyl peroxide. Also, the effects of molecular weight of liquid natural rubber (LNR) as a compatibilizer were studied. The degree of compatibilization between NBR and NR is determined indirectly through measurements of mechanical properties and impact resistance. The maleic anhydride and benzoyl peroxide concentrations influence the mechanical properties and impact resistance of the blends. Also, the mechanical properties of the blends showed that the molecular weight of LNR played an important role in determing their performance. Copyright © 2004 John Wiley & Sons, Ltd.     

ON THE KINETICS AND MECHANISM OF THE COPOLYMERIZATION OF ACRYLONITRILE WITH STYRENE IN THE PRESENCE OF COPPER CHLORIDE

The copolymerization of styrene (St) and acrylonitrile (AN) complexed with CuCl_2 monomer by a free radicalmechanism was performed using benzoyl peroxide as an initiator at 65℃ under N_2 atmosphere for 150 min. The rate ofpolymerization (R_p) was found to increase linearly with the concentration (in mol/L) of CuCl_2, AN and St through scalingrelations. The activation energy of the copolymerization process in the presence and absence of CuCl_2 was found to be46.5 kJ/mol and 102 kJ/mol, respectively. The viscosity average molecular weigh of the copolymer and the k_p~2/k_t ratio weredctermired to further assess the accelerating effect of CuCl_2 on the copolymerization process. The copolymerization processin the presence of CuCl_2 has a radical complex mechanism.     

Effect of the Formation of Inclusion Complexes With β-Cyclodextrin on the Photoisomerization and Fluorescence Properties of Aromatic Norbornadiene Derivatives

The valence photoisomerization of four aromatic norbornadiene (NBD)derivatives has been studied in ethanol and in 0.01 M -cyclodextrin(-CD) water–ethanol (v/v, 99/1) solution (WECD). Observedfirst-order rate constants are found to be of the same order of magnitude inethanol and WECD, ranging between 0.1 and 0.28 s^-1, accordingto the compound. These photoisomerization kinetic properties are attributedto the formation of inclusion complexes between NBDs and -CD. Thestoichiometry is 1 : 1, and association constants ranging between 310 and390 M^-1 have been determined fluorimetrically, usingBenesi–Hildebrand plots and a nonlinear regression method. Thestructure of the inclusion complexes is discussed on the basis of AMIsemiempirical dimension calculations and photophysical properties.     

Electrical conductivity,spectral and magnetic properties of some transition metal complexes derived from dimedone bis(4-phenylthiosemicarbazone)

Summary Co^II, Ni^II, Cu^II, Zn^II, Cd^II and U^VIO₂ complexes of 5, 5-dimethyl-1, 3-cyclohexanone bis(4-phenylthiosemicarbazone), H₂CPT, have been characterized by elemental analysis, i.r. and reflectance spectral studies, and magnetic moment measurements. I.r. spectra show that H₂CPT gives rise to dibasic quadridentate SNNS donor. A square-planar structure is proposed for the copper(II) complex and octahedral for cobalt(II) and nickel(II) complexes according to the magnetic and electronic spectral data. The electrical conductivities of H₂CPT and its CO^II, Ni^II, Cu^II and Cd^II complexes were measured. The positive temperature coefficient (d/dT) and the higher activation energies of H₂CPT and its Cd^II and Cu^II complexes is evidence of their semiconducting character.     

Synthesis of Spiro and Fused Five Membered N-Heterocycles from Alkylidenephosphoranes

Triketoindan-2-oxime reacted readily with ethoxycarbonylmethylene triphenylphosphorane to give mainly the corresponding spiro-pyrrole (38%) along with the fused 1-hydroxydihydropyrrole (14%), whereas the spiro-dimer (29%) was obtained from the reaction of the oxime with methoxycarbonylmethylenetriphenyl phosphorane in addition to the corresponding 1-hydroxydihydropyrrole (31%). Conversely, Wittig products, mono-olefin (52%) and diolefin (<7%) along with the reduced substrate (10%), were observed when the oxime was treated with a cyano ylide. The reactions of the oxime with allyl- and vinyl phosphonium salts proceeded under phase-transfer catalysis to afford fused oxazole (46%) and spiro[2]oxazole (17%), while with the latter the fused 1-hydroxypyrrole (55%) was produced.     

STOP: A slater-type orbital package for molecular electronic structure determination

A general ab initio package using Slater-type atomic orbitals is presented. This package, called STOP, uses the one-center two-range expansion method to evaluate the multicenter electronic integrals. Thoroughly optimized numerical techniques, in particular, convergence accelerators and suitable Gauss quadratures, are used in the algorithms which provide accurate numerical values for all these integrals. STOP thus provides wavefunctions for general molecular structures at the self-consistent field level for the first time over a Slater-type orbital basis. © 1996 John Wiley & Sons, Inc.     

An interior-proximal method for convex linearly constrained problems and its extension to variational inequalities

In this paper, an entropy-like proximal method for the minimization of a convex function subject to positivity constraints is extended to an interior algorithm in two directions. First, to general linearly constrained convex minimization problems and second, to variational inequalities on polyhedra. For linear programming, numerical results are presented and quadratic convergence is established.Corresponding author. His research has been supported by C.E.E grants: CI1* CT 92-0046.