Competing reactions of hydrophenylation and phenylation in tetraphenylantimony chloride methyl acrylate palladium chloride system

A new catalytic reaction of the competing phenylation and hydrophenylation in air of methyl acrylate with tetraphenylantimony chloride in the presence of PdCl₂ (0.04 mol per 1 mol of organometallic compound) in acetonitrile at 50°C for 6 h was studied. The yields of methyl cynnamate and methyl hydrocynnamate were 0.73 and 0.27 mol mol^?1 respectively. The products ratio obtained depends slightly on the process duration, the Ph₄SbCl and methyl acrylate ratio, and the structure of Pd salt [PdCl₂, Pd(OAc)₂, Li₂PdCl₄], but significantly on the nature of a solvent (MeCN > DMF > THF). The use of Ph₄SbCl instead of Ph₄SbBr leads to decrease in the yield of methyl hydrocynnamate to 0.04 mol mol^?1. In the reactions of Ph₄SbX (X = F, I, OAc, O₂CEt) the product is not formed at all.     

Synthesis of 1,2,4-triazolo[3,2-b]-1,3-thiazines

1,2,4-Triazolo[3,2-b]-1,3-thiazines were obtained by the reaction of 1,2,4,-triazole-3-thiones with an equimolar amount of 1-phenyl-2-cyanoacetylene in the presence of triethylamine or potassium hydroxide. It is shown that triazolethiones form N,S diadducts upon reaction with a twofold excess of cyanoacetylene. The nature of the heteroatom in the exo position of the heteroring affects the direction of addition to phenylcyanoacetylene. 2,4-Bis(1-phenyl-2-cyanovinylene)-1,2,4-triazol-3-one was synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1051–1053, August, 1982.     

Reaction of 2-methyl-6-p-bromophenyl-3,5-hexadiyn-2-ol with alcohols and ketones

Conclusions The nucleophilic addition of alcohols and ketones to a p-bromophenyldiacetylenic alcohol leads respectively to p-bromophenylenyne ethers and dioxolanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2827–2829, December, 1974.     

3D hydrogen bond thermodynamics (HYBOT) potentials in molecular modelling

A new approach is proposed to more accurately estimate the energies of H-bond interactions in three-dimensional (3D) molecular modelling. The approach is based on the use of H-bond acceptor and donor enthalpy factor values calculated by means of program HYBOT, the use of a sigmoid relationship to determine the optimum H-bond distances and established force-field methods to determine distance and angle dependencies. The base-pair interactions in a short A-form RNA double-helix are presented as an example of enthalpy calculations of hydrogen bonding for a model system.     

Cyanoacetylene and its derivatives 2. Reaction of isomeric cyanomethylacetylene-cyanoallene with glycols

Conclusions The reaction of isomeric cyanomethylacetylene-cyanoallene with glycols gives cyclic acetals and glycol mono- and diethers as a result of nucleophilic attack on the central atom of the allene system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 398–401, February, 1979.     

Hydrosilylation of Vinylsiloxanes with Hydrosiloxanes in the Presence of Thermo- and Photoactivated Platinum(II) Phosphine Complexes

Catalytic properties of thermo- and photoactivated platinum complexes [Pt(R₂R'X)₂Cl₂] (X = P, R = Me, R' = Ph; X = P, As, Sb, R = R' = Ph or Bu) in hydrosilylation of vinylsiloxanes with hydrosiloxanes were studied. The neutral ligands were ranked in terms of their effect on the activity of the catalysts. A mechanism of hydrosilylation was proposed.     

Perron type integral on compact zero-dimensional Abelian groups

Perron and Henstock type integrals defined directly on a compact zero-dimensional Abelian group are studied. It is proved that the considered Perron type integral defined by continuous majorants and minorants is equivalent to the integral defined in the same way, but without assumption on continuity of majorants and minorants.     

An efficient scheme for the implementation of implicit Runge-Kutta methods

A scheme is proposed for solving nonlinear algebraic equations arising in the implementation of the implicit Runge-Kutta methods. In contrast to the available schemes, not only the starting values of the variables but also those of the derivatives are predicted. This makes it possible to reduce the number of evaluations of the function (the right-hand side) at each implicit stage without significantly reducing the accuracy of integration.     

The escape transition of a polymer: A unique case of non-equivalence between statistical ensembles

A flexible polymer chain under good solvent conditions, end-grafted on a flat repulsive substrate surface and compressed by a piston of circular cross-section with radius L may undergo the so-called “escape transition” when the height of the piston D above the substrate and the chain length N are in a suitable range. In this transition, the chain conformation changes from a quasi-two-dimensional self-avoiding walk of “blobs” of diameter D to an inhomogeneous “flower” state, consisting of a “stem” (stretched string of blobs extending from the grafting site to the piston border) and a “crown” outside of the confining piston. The theory of this transition is developed using a Landau free-energy approach, based on a suitably defined (global) order parameter and taking also effects due to the finite chain length N into account. The parameters of the theory are determined in terms of known properties of limiting cases (unconfined mushroom, chain confined between infinite parallel walls). Due to the non-existence of a local order parameter density, the transition has very unconventional properties (negative compressibility in equilibrium, non-equivalence between statistical ensembles in the thermodynamic limit, etc.). The reasons for this very unusual behavior are discussed in detail. Using Molecular Dynamics (MD) simulation for a simple bead-spring model, with N in the range 50 N 300 , a comprehensive study of both static and dynamic properties of the polymer chain was performed. Even though for the considered rather short chains the escape transition is still strongly rounded, the order parameter distribution does reveal the emerging transition clearly. Time autocorrelation functions of the order parameter and first passage times and their distribution indicate clearly the strong slowing down associated with the chain escape. The theory developed here is in good agreement with all these simulation results.     

Absolute frequency measurement of iodine lines with a femtosecond optical synthesizer

We have used a single laser femtosecond optical frequency synthesizer together with a widely tunable Nd:YAG laser to measure the absolute frequency of several absorption lines in molecular iodine around 532 nm. The use of two different repetition frequencies allows us to determine the number of modes used for the frequency measurement unambiguously. The lines also provide data for the determination of improved ro-vibrational constants of the iodine molecule. Received: 3 July 2001 / Published online: 19 September 2001