Synthesis of fused polycyclic aromatics by palladium-catalyzed annulation of arynes using 2-halobiaryls

The Pd-catalyzed annulation of arynes by 2-halobiaryls and related vinylic halides provides a very efficient, high yielding synthesis of polycyclic aromatic and heteroaromatic hydrocarbons. This process appears to involve the catalytic, stepwise coupling of two very reactive substrates, an aryne and an organopalladium species, to generate excellent yields of cross-coupled products.     

NMR-Untersuchungen an Methylphosphoniumchlorid

N.M.R. Investigation of Methylphosphonium Chloride The n.m.r. spectra of [CH₃PH₃]Cl in aqueous hydrochloric acid as solvent and of [OP(CH₃) (OCH₂CH₂Cl)OCH₂? ]₂ in C₆D₆ und CD₂Cl₂ are described. ³¹P n.m.r. resonances with a line width at half height of 55 Hz are found for the H₂O? HCl solutions of [CH₃PH₃]Cl in the solid state at 183 K.     

Crystallization impedance in the case of D.C. superposition

An expression for the impedance frequency dependence in the case of d.c. superposition has been derived and analyzed for the crystallization process of metals taking into account the two-dimensional diffusion of ions in solution and the surface diffusion of adatoms and using the simplest surface model with parallel step lines. It is shown that in the general case it is impossible to present the crystallization impedance as the sum of the surface diffusion impedance and the Warburg impedance. It has been found that in the case of anode polarization an unusual effect of the impedance increasing with agitation intensity takes place which is typical of this mechanism. Possible methods for determination of the model parameters from impedance measurements are discussed. The authors suggest an iteration procedure which permits to determine all the parameters of the model under consideration including the surface diffusion coefficient of adatoms and the spacing between the growth step lines.     

Electromagnetic interactions with rough metal surfaces

When surfaces are structured on the scale of the wavelength, we can expect incident light to be strongly modified by the surface. This is especially the case when the surface is metallic. We have developed a formalism for computing these modifications, closely analogous to electron scattering theory, which we briefly review and present some results for optical properties of, and electron energy loss in, colloids. Our main theme is another effect associate with rough or structured metallic surfaces: Surface Enhanced Raman Scattering, or SERS. We model the rough surface by a periodic array of spheres and obtain the correct magnitude for the enhancement and for the frequency shifts observed.     

Oxidative addition of some geminal halonitroalkanes to iridium(I) and platinum(0) compounds

Oxidative addition of 1-chloro-1-nitroethane to trans-IrCl(CO)-[P(CH₃)₂C₆H₅]₂ followed by treatment of the initial product with pyridine yields a new iridium(III) complex IrCl(py)[COC(NO₂)CH₃][P(CH₃)₂C₆H₅]₂, whose structure has been confirmed by X-rays crystallography. Two intermediate products have been observed by NMR spectroscopy; their structures have been tentatively assigned. The reaction of the corresponding bromine derivatives yields two isomers of the composition IrBr₂(CO)[CH(NO₂)CH₃][P(CH₃)₂C₆H₅]₂, and these are not affected by pyridine. The reaction of 1-chloro-1-nitroethane with Pt[P(C₆H₅)₃]₄ takes a completely different course in that yields nitrorethane and cis-PtCl₂[P(C₆H₅)₃]₂ as the main products, with no detectable formation of the products of oxidation addition. A brief mechanistic investigation points towards the participation of radicals and radical anions as transient intermediates and a mechanism is proposed which explains most of the experimental results.     

Fluorine absorption spectra and some fluorides in condensed state

The absorption spectra of liquid F₂, NF₃, N₂F₄, CF₄, BF₃, NF₃, SF₆ have been obtained at diminished temperatures in the near ultra-violet region of the spectrum. It is shown that the absorption spectrum does not differ from the spectra in the gaseous phase, therefore the elementary absorption act is characterized by the cross section of photon absorption by an individual molecule. The absorption cross sections of the above mentioned molecules are represented in the liquid phase, which do not differ strongly from absorption cross sections of these molecules in the gaseous phase. The dependence of the absorption cross sections of liquid fluorine on its concentrations in solutions with N₂, Ar, NF₃, O₂ at - 196°C has been studied. The cross sections of photon absorption by the fluoride molecule in different liquid media with small fluorine concentrations have been obtained.     

Separation of molybdenum from tungsten with di(2-ethylhexyl)-phosphoric acid ac extractant

The use of di(2-ethylhexyl)phosphoric acid (HDEHP) as an extractant for the separation of molybdenum from tungsten was examined with the help of molybdenum-99 and tungsten-187 as radiotracers. Effective separation was obtained when the aqueous phase contained phosphoric acid at pH 0.8–2 or pH 3–3.5, depending on the amounts of metal. The method is applicable to both tracer and milligram amounts of molybdenum. The structure of the extracted species was examined by infrared spectroscopy.     

Synthetic and modified isoflavonoids XVII. Interaction of synthetic analogs of isoflavones with guanidine

Under the influence of guanidine, 1,3-benzodioxolane, 1,4-benzodioxane, and 1,5-benzodioxepane analogs of isoflavone are converted into 2-aminopyrimidine derivativesTranslated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 636–640, September–October, 1994.     

Proper determination of order of reactions by thermal analysis

The relationship 1– _m=1.062n ^1/1–n , well-known in non-isothermal kinetics and applied for determination of the kinetic exponentn, is not universal. A more accurate modification of the given equation is proposed in the form of a more complex function 1– _m=(n, X_m), whereX _m =E/RT _m is the dimensionless Arrhenius' criterion.