Cure kinetics of a cobalt catalysed dicyanate ester monomer in air and argon atmospheres from DSC data

A kinetic analysis of the cyclotrimerisation reaction of a dicyanate ester monomer catalysed by cobalt(II) acetylacetonate and nonylphenol in air and argon atmospheres has been carried out by differential scanning calorimetry (DSC). Dynamic and isothermal DSC scans as well as the glass transition temperature are the experimental data obtained. From isothermal scans a higher cyanate conversion in air than in argon was obtained. The cyanate conversions are satisfactorily described with a second-order kinetic equation in the kinetically controlled region, and by m-order (m<1) equation after vitrification is reached. Activation energies determined by different procedures agree among them, showing slightly higher values in argon than in air.     

Coordination of N-Substituted Porphyrins with Simple and Chelate Zinc Salts in DMSO

The effect of peripheral substitution in the porphyrin macrocycle (₂OEtP, H₂TPP) of the nature of the N-substituent (X = Me, Ph) and of the anion in the salt solvate (A = ^–, NO₃ ^–, ^–) on the complexation of the N-substituted porphyrins with zinc salts in DMSO is studied. The positions of the bands in the electronic absorption spectrum of the (A)M(N-X)P metal complex were found to depend only slightly on the nature of the A anion in the composition of the coordination sphere of the complex. An inhibition of coordination of the N-substituted ₂TPP derivatives by zinc nitrate was discovered that is not typical of porphyrins proper. The type of hybridization of the substituted nitrogen atom in the porphyrin molecule is discussed. A mixed type of hybridization is suggested: the sp ²- and p ³-forms in the ligands and an almost complete transition to the p ³ form in the N-substituted metal complexes.     

A methodology for synthesis of primary o-phenylenebisphosphines and o-chlorophenylphosphines

On the basis of the reaction of ethynediylbisphosphonates and chloroethynylphosphonates with classical donor alka-1,3-dienes, a general strategy for synthesis of o-bisphosphanylbenzenes and o-chlorophosphanylbenzenes, which includes two consecutive steps: Diels-Alder condensation → aromatization of the carbocyclic phosphonate (bisphosphonate) formed → reduction of the phosphonate groups, was developed. Convenient procedures are devised for aromatization of phosphorus-containing cyclohexa-1,4-dienes and for reduction of o-phenylenebisphosphonates and o-clorophenylphosphonates to primary phosphines. A series of new alkylsubstituted phosphonic chlorides were prepared, and a possibility of functionalization of methylsubstituted o-phenylenebisphosphonates and o-clorophenylphosphonates by the methyl groups is demonstrated.     

Phytoecdysteroids of plants of the genusSilene XIV. Brahuisterone fromSilene brahuica

A new ecdysteroid with the composition C₂₇H₄₄O₆ which has been called brahuisterone has been isolated from the epigeal part of the plantSilene brahuica Boiss. Its chemical and complete spatial structures have been established by spectral studies and the x-ray structural method (diffractometer, Cu-K radiations, 996 reflections, direct method, R=0.119).Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbekistan Republic, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 553–558, July–August, 1993.     

Structure and reactivity of benzothiazole-2-thione polysulfides

A quantum-chemical study was made of the possibility of the formation of polysulfides from benzothiazole-2-thione and their structure. The reactivity indices of the benzothiazole-2-thione molecule and of the small sulfur fragments were calculated. It was shown that as the fragments approach each other the formation of polysulfide structures with increased reactivity becomes possible.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 73–78, January–February, 1990.     

A method for the rapid calculation of matrix elements with highly oscillatory JWKB radial wavefunctions

A method for the rapid computation of matrix elements with JWKB radial wavefunctions is discussed. The method consists of dividing the range of integration into segments determined by the nodes of the semiclassical wavefunction. The desired matrix elements are calculated by summing the contributions from each segment which are evaluated by integrating between nodes with a Gauss-Mehler quadrature formula. The results are compared with exact quantum mechanical calculations and were found to agree within 1–2%. The calculations with the present method were generally five to ten times faster than the quantum mechanical calculations.     

On the charge transfer in the process of adsorption at the electrode/solution interface: Remarks on the paper “experimental determination and interpretation of the electrosorption valency γ” by J. Schultze and K. Vetter

A critical analysis shows that the approach to the estimation of the charge transfer in the process of adsorption at the electrode/solution interface used by Vetter and Schultze in the general case is not justified without introduction of non-thermodynamic models. This approach can prove useful in the investigation of the electric double layer within the limits of applicability of Grahame's model. A number of cases can however be cited where the approach of Schultze and Vetter is inapplicable. The conclusions of Schultze and Vetter regarding the adsorption of hydrogen at platinum are apparently based on some misunderstanding. In this case the thermodynamic approach^{6, 23} should be used.It would be more correct to call the quantity γ “the formal coefficient of charge transfer”, rather than “the electrosorption valency”.     

Reaction of epoxy compounds with salts of thioacids

Conclusions 1. When the alkali metal salts or the ammonium salts of O,O-dialkyl thiophosphates or O,O-dialkyl dithiophosphates are reacted with epoxy compounds the latter undergo thioepoxidation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 353–358, February, 1971.     

Synthesis of some mixed esters of thiophosphoric acid

Summary Six esters of O,O-dialkyl S-carbalkoxymethylphosphinic acids that have not been described in the literature were prepared and their structures demonstrated.     

Comparative evaluation of quantum-chemical methods for calculating aromatic and antiaromatic nitrogen heterocycles (review)

The possibilities of quantum-chemical methods in the determination of characteristics of aromatic and antiaromatic nitrogen heterocycles such as the thermodynamic stabilities, geometries of the molecules, electron distributions, dipole moments, ionization potentials, electron and proton affinities, energies and geometries of the molecules in the excited states, electronic spectra, and reactivities are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1587–1603, December, 1989.