Approximate calculation of the matrix elements of Coulomb and exchange operators for the “core” electrons of the atoms Rb through Cd

Following a previously described method which approximates the Coulomb and exchange integrals in valence-electron-only SCF calculations, the necessary parameters for the atoms from Rb to Cd are reported. Extension to other atoms is in progress.     

Synthèse de l'acide décarboxythamnolique

Synthesis of Decarboxythamnolic Acid The total synthesis of the meta-depside decarboxythamnolic ( = 3-[(3-formyl-2-4-dihydroxy-6-methyl-phenyl)oxy]-2-hydroxy-6-methoxy-4-methylbenzoic acid; 25 ) by the biomimetic condensation of the substituted β-orcinol units 9 and 22 is described.     

Effect of a Weak Electrolyte on the Critical Micellar Concentration of Sodium Dodecyl Sulfate

The critical micellar concentration of sodium dodecyl sulfate is strongly altered bytris(hydroxy-methyl)methylammonium ions. The effect of buffer solutions containing this weak electrolyte as the counterion source has been studied using various concentrations of the acid–base system as well as modifying the pH. Results show that counterion concentrations ranging from 0 to 340 × 10⁻³M induce an appreciable diminution of the critical micellar concentration from 8 to 0.7 × 10⁻³M. The analysis of data suggests that the critical micellar concentration of sodium dodecyl sulfate depends on the concentration of weak electrolytes in a way very similar to that of strong electrolytes.     

Determination of the perpendicular magnetic parameters for Cu(II) EPR spectra from angular anomalies

A method is outlined to obtain accurate values of g_? and A_? in EPR spectra of Cu(II) compounds, provided that an extra absorption peak due to an angular anomaly can easily be recognized. This method turns out to be useful especially in the case of low resolution and in the presence of a superhyperfine pattern due to the ligands.     

Preparation and structural characterization of polymer-supported methylrhenium trioxide systems as efficient and selective catalysts for the epoxidation of olefins

Novel heterogeneous compounds of methylrhenium trioxide (MTO) were prepared with poly(4-vinylpyridine) and polystyrene as polymeric supports. The wide-angle X-ray diffraction (WAXS.) analysis, performed by the application of the difference method, showed, in a representative case of the poly(4-vinylpyridine)/MTO derivatives, a slightly distorted octahedral conformation on the metal's primary coordination sphere. The Re-O and Re-C bond distances were not influenced by the polymeric nature of the ligand, while the Re-N bond distance was abnormally shorter than those previously observed for homogeneous MTO/L(n) complexes, showing a strong coordination of the rhenium atom to the support. A set of scanning electron microscopy (SEM) photographs showing the morphology of the surface of particles of poly(4-vinylpyridine)/MTO and polystyrene/MTO systems are reported. The reticulation grade of the polymer was a crucial factor for the morphology of the particles surface. Poly(4-vinylpyridine) 2% cross-linked systems were characterized by particles with very irregular shape and surface. Poly(4-vinylpyridine) 25% cross-linked systems showed particles with regular spherical shape, which morphology was similar to microcapsules obtained with polystyrene. All novel MTO compounds were efficient and selective heterogeneous catalysts for the epoxidation of olefins using environmentally friendly H2O2 as oxygen atom donor. The catalyst activity was maintained for at least five recycling experiments.     

Synthèse de l'évernine

Synthesis of Evernin Two syntheses of the depside evernin 6 are described. Condensation of methyl acetoacetate and methyl crotonate followed by aromatization and reduction with Raney-Ni led to methyl orsellinate (3) . The condensation of everninic acid (4) , obtained by partial methylation of 3 and saponification of the methyl ester, with methyl 2, 4-dihydroxy-3, 6-dimethylbenzoate (methyl β-orcin carboxylate) (5) in presence of cyclohexylcarbodiimide gave evernin ( 6 ). In a second syntheis methyl dihydroorsellinate (1) was regiospecifically converted into its 4-methyl enol ether and aromatized via the benzene selenenyl derivative to yield methyl evernate (7) . Benzylation followed by saponification gave the free acid 8 . Methyl β-orcin carboxylate (5) was synthesized in an analogous way from methyl 3,6-dimethyl-2,4-dioxocyclohexanecarboxylate. Condensation of 8 with the methyl ester 5 by treatment with trifluoroacetic anhydride in toluene yielded 9 , which could be converted into evernin ( 6 ) by hydrogenolysis of the benzyl ether.     

Synthesis,spectroscopic, magnetic,conductometric and electro-chemical investigations of nickel(II)-1-phenyl-4,6-dimethylpyrimidine-2-thione complexes

Summary Tris-, bis- and mono-ligand complexes of Ni^II with 1-phenyl-4, 6-dimethylpyrimidine-2-thione (L) having the general formulae NiL₃X₂·2H₂O (X = ClO _inf4 ^p– , BF _inf4 ^p– ), NiL₂X₂ (X = Cl^–, Br^–, SCN^– or NO _inf3 ^p– ), NiL₂X₂·EtOAc (X = Br^– or I^–), NiL₂X₂·H₂O·EtOH (X = I^– or NO _inf3 ^p– ) and NiLCl₂·3H₂O, were synthesized and their structures deduced from i.r. and electronic spectra, and magnetic properties. The combined evidence is consistent with an octahedral coordination for the Ni^II ion in all the complexes, with the ligand acting as a bidentate N,S-chelating agent. Spectral evidence, conductivity data and electro-chemical results in DMF solution show that the complexes undergo solvolysis readily. Polarographic and c.v. data for the [NiL₃](ClO₄)₂·2H₂O complex and for the [Ni-(DMF)₆](ClO₄)₂-L systems, at increasing ligand concentrations, have shown that in DMF solution the [Ni(DMF)₆]²⁺ cation prevails and that the thiopyrimidine-containing species, [NiL(DMF)₅]²⁺ (L = N-monodentate ligand) , can be formed only in the presence of a large excess of free ligand.Author to whom all correspondence should be directed.     

Ozonation of Thioamide Containing Heterocycles. A New General and Selective Procedure for the Synthesis of C-2 Substituted Heteroazole Derivatives

2-Mercaptoheterazoles readily react with ozone in the presence of nucleophiles and under mild experimental conditions to form several C-2 substituted heterazoles.