General method for dehydration, intramolecular cyclization, and fluorination of trifluoromethyl-1H-pyrazoles using DAST

In this study, the versatile diethylaminosulfur trifluoride (DAST), a well-known fluorinating agent, was applied in the dehydration, intramolecular cyclization, and mono- and difluorination reactions of some 5-trifluoromethyl-1H-pyrazoles and 2-pyrazolines employing a general, mild, and efficient methodology. The azole precursors were synthesized from the reactions of acyclic and cyclic trifluoroacetylated enol ethers with hydrazines [NH₂NHR, where R = C₆H₅, C₆F₅, 2-Furanoyl] and showed a differentiated chemical behavior in the presence of DAST.     

Classical and fractal analysis of vehicle demand on the ferry-boat system

Transportation problems are important complex systems because of the increased number of vehicles in cities. In this paper, we study time series of vehicle demand by using the ferry-boat system between Salvador city and Itaparica island, in Bahia, Brazil. We compare the traditional demand analysis (ARIMA method) with the self-affine ones (the scaling exponent α and the density of crossing points ρ). In addition, taking into account the inherent self-affine behavior we study the stationary states of this dynamic process by using a nonlinear Fokker-Planck equation. The present findings indicate that the scaling exponent α describes some properties of flux of vehicles using the ferry-boat system. The behavior of α gives an alternative explanation about demand analysis, and the nonlinear Fokker-Planck equation presents a solution close to the stationary behavior of this complex dynamical analysis.     

Reinforcement of elastomeric networks by fillers

Although numerous investigations have been devoted to the analysis of filled systems, the mechanisms of the reinforcement have not been completely clarified. The present paper attempts to recall, through new experimental data, some of the basic mechanisms of filler reinforcement. The basic processes giving rise to the increase in the elastic modulus, generally observed by a filler addition in an elastomeric medium, are discussed in the light of mechanical measurements and of recent results based on measurements of chain orientation.     

Fluorenyl based syndiotactic specific metallocene catalysts structural features,origin of syndiospecificity

The stereochemistry of propylene insertion/propagation reactions with a variety of C_s symmetric fluorenyl- containing single site catalysts is discussed. Our recent results indicate that independent of the chemical composition of the ancillary ligand fragments, or nature of the transition metal, active sites with local C_s symmetry and enantiotopic coordination positions behave syndioselectively in the general context of chain migratory insertion mechanism. Perfect bilateral symmetry neither exists nor is required in these processes. In this context the mechanism of syndiospecific polymerization is revisited by taking into account the structural characteristics and catalytic behavior of the original metallocene based (η⁵-C₅H₄-CMe₂-η⁵-C₁₃H₈) MCl₂/ MAO; M = Zr ( 1 ), Hf ( 2 ) catalyst systems and new syndiotactic specific systems including (η⁵-C₅H₄-CPh2-η5-3,6-di-tBut-C₁₃H₆)ZrCl₂ ( 3 ), η¹,η⁵-(μMe₂Si)(3,6-di-tBut-Flu)(t-ButN)MCl₂/ MAO; M =Ti ( 4 ), Zr ( 5 ) and η¹,η⁵-(μMe₂Si)(2,7-di-tBut-Flu)(t-ButN)MCl₂/ MAO; M = Ti ( 6 ), Zr ( 7 ).