Allene-alkyne cross-coupling for stereoselective synthesis of substituted 1,4-dienes and cross-conjugated trienes

Titanium-mediated cross-coupling of allenic alcohols with alkynes has been investigated. Divergent reaction pathways were discovered that provide either stereodefined 1,4-dienes or substituted cross-conjugated trienes. In short, allene substitution plays a critical role in the determination of reaction pathway.     

Allene-alkyne cross-coupling for stereoselective synthesis of substituted 1,4-dienes and cross-conjugated trienes

Titanium-mediated cross-coupling of allenic alcohols with alkynes has been investigated. Divergent reaction pathways were discovered that provide either stereodefined 1,4-dienes or substituted cross-conjugated trienes. In short, allene substitution plays a critical role in the determination of reaction pathway.     

Determination of zinc by flow injection with fluorimetric detection in a micellar medium

A room-temperature flow injection spectrofluorimetric method is presented for the determination of Zn(II), based on the use of salicylaldehyde thiocarbohydrazone in the presence of Triton X-100 and sodium acetate-acetic acid buffer. Various physical and chemical variables affecting the reaction in the flow system were evaluated. The proposed method is very selective. The calibration graph is linear over the range 10–1000 ng/ml, with a detection limit of 5 ng/ml and a relative standard deviation at the 50 ng/ml level of 1.8 %. The method was successfully applied to the determination of Zn(II) in drinking waters and biological samples.     

Micellar effects on a ligand substitution reaction: Kinetics of the formation of [Fe(CN)5(μ‐pz)Ru(NH3)5]−, from [Fe(CN)5H2O]3− and [Ru(NH3)5pz]2+, in the presence of anionic micelles

The kinetics of substitution of H₂O by Ru(NH₃)₅pz²⁺ (pz = pyrazine) in Fe(CN)₅H₂O^3? have been studied in micellar aqueous solutions of sodium dodecylsulfate (SDS). Experimental results are discussed by using an approach based on the transition‐state theory. This approach is better than others based on the pseudophase model, which can also be used, because it is able to give a clear meaning to the parameters of the model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants to the micelles (Ru(NH₃)₅pz²⁺ in the present work). This association is governed by an equilibrium constant that depends on the electrostatic potential at the surface of the micelles. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 627–633, 2004     

Dynamical stability and pure thermodynamic phases

A notion of stability of dynamics under distant perturbations is introduced. It is demonstrated, for quasi-local systems, that the stability of an equilibrium state under the same perturbations implies the state is factorial, i.e. strongly clustering in space. We also characterize the set of perturbations necessary to ensure the equivalence of stability and factorialness.     

1H,4H-1,4-Diphenylpyridazino[1,2-α]pyridazine-6, 9-dione

Crystals of C₂₀H₁₆N₂O₂ are orthorombic:P2₁2₁2₁,a = 28.1364(21),b = 7.6474(2),c = 7.5376(2) Å,Z = 4, = 6.4 cm^–1 (CuK radiation), andM = 316.36. The structure has been solved by direct methods and refined by two-block least-squares toR = R _w = 0.042. The conformation of ringB is a distorted envelope at N(10), and the phenyl rings have acis configuration with respect to the pyridazine ring. Thermal motion of the molecule has been analyzed in terms of the rigid-body TLS model.On leave from Departamento de Fisica, Facultad de Ciencias Exactas, U.N.L.P., calle 115 esq. 49, La Plata, Buenos Aires, Argentina.