Régio et périsélectivité de réactions de diels-alder et des cycloadditions dipolaires-1,3 avec une triazépine-1,2,4: Approche théorique

e.s The cycloaddition of 1,3-dipoles (mesitonitrile, C,N-dimethylnitrone) and various dienophiles (DMAD, maleic anhydride) to 1,2,4-triazepine 1 are peri and regiospecific. Nitrone excepted the preferred orientation of addition is predicted correctly by FMO/MNDO calculation.     

Natural convection of non-Newtonian power law fluids in a shallow horizontal rectangular cavity uniformly heated from below

Analytical and numerical study is conducted for two-dimensional steady-state buoyancy driven flow of a non-Newtonian power law fluid confined in a shallow rectangular horizontal cavity uniformly heated from below, while its short vertical rigid sides are considered adiabatic. The effect of the non-Newtonian behaviour on the onset of convection, fluid flow, temperature field, and heat transfer is examined. A closed approximate analytical solution is developed on the basis of the parallel flow assumption and the obtained results are validated numerically by solving the full governing equations.     

Nouvelles synthèses de systèmes bicycliques hétéroaromatiques. I. Cycloaddition [4 + 2]π de la diméthyl-2,7 diméthylthio-3,5 triazépine-1,2,4

The cycloaddition of 3,5-dimethylthio-1,2,4-triazepine (1) to various dienophiles has been studied. 4-Phenyl-1,2,4-triazoline-3,5-dione, dimethyl acetylene dicarboxylate and meleic anhydride react with I to give the [4+2]π cycloadduct. The heterocyclic products were found to be formed via 1,3-sigmatropic rearrangement of this cycloadduct.     

Mixed-ligand organometallic polymers containing the "Pd(2)(dmb)2(2+)" fragment: properties of the [Pd2(dmb)2(diphos)2+](n) polymers/oligomers in solution and in the solid state

The 1:1 reaction between the d(9)-d(9) Pd(2)(dmb)(2)Cl(2) complex (dmb = 1,8-diisocyano-p-menthane) and the diphosphine ligands (diphos) bis(diphenylphosphino)butane (5, dppb), bis(diphenylphosphino)pentane (6, dpppen), bis(diphenylphosphino)hexane (7, dpph), and bis(diphenylphosphino)acetylene (8, dpa) in the presence of LiClO(4) leads to the [[Pd(2)(dmb)(2)(diphos)](ClO(4))(2)](n) polymers. These new materials are characterized by NMR ((1)H, (13)C, (31)P), IR, Raman, and UV-vis spectroscopies (466 < lambda(max)(dsigma-dsigma*) < 480 nm), by ATG, XRD, and DSC methods, and by the capacity to make stand-alone films. From the measurements of the intrinsic viscosity in acetonitrile, the M(n) ranges from 16000 to 18400 (12 to 16 units). The dinuclear model complex [Pd(2)(dmb)(2)(PPh(3))(2)](ClO(4))(2) (4) is prepared and investigated as well. The molecular dynamic of the title polymers in acetonitrile solution is investigated by means of (13)C spin-lattice relaxation time (T(1)) and nuclear Overhauser enhancement methods (NOE). The number of units determined by T(1)/NOE methods is 3 to 4 times less than that found from the measurements of intrinsic viscosity, and is due to flexibility in the polymer backbone, even for bridging ligands containing only one (dmb) or two C-C single bonds (dpa). During the course of this study, the starting material Pd(2)(dmb)(2)Cl(2) was reinvestigated after evidence for oligomers in the MALDI-TOF spectrum was noticed. In solution, this d(9)-d(9) species is a binuclear complex (T(1)/NOE). This result suggests that the structure of the title polymers in solution and in the solid state may not be the same either. Finally, these polymers are strongly luminescent in PrCN glasses at 77 K, and the photophysical data (emission lifetimes, 1.50 < tau(e) < 2.75 ns; quantum yields, 0.026 < Phi(e) < 0.17) are presented. X-ray data for [Pd(2)(dppe)(2)(dmb)(2)](PF(6))(4): monoclinic, space group C2/c, a = 24.3735 A, b = 21.8576(13) A, c = 18.0034(9) A, b = 119.775(1) degrees, V = 8325.0(8) A(3), Z = 4.     

Ultraviolet-visible spectroscopic study of 3,5-dithio-2,7-dimethyl-[1,2,4]-triazepine: qualitative analysis of tautomeric behaviour

Room temperature UV-vis absorption spectra of the tautomeric system 3,5-dithio-2,7-dimethyl-[1,2,4]-triazepine in solution, in acetonitrile (CH3CN), are measured at different water volume percentages. The comparison of the obtained measures to the calculated allowed absorption transitions, using ZINDO/S package, reveals the coexistence of all the tautomeric forms in aprotic polar solution with a high dominance of the dithione form. The solute-water hydrogen bond, which seems to be of 1:n-type, favours the dithiol and monothiol conformers to the detriment of the dithione one. Further experimental investigations lead to the result that standing at ambient Laboratory conditions in the dark favours the dithione tautomeric isomer, while standing at indirect sunlight shifts the tautomeric equilibrium away from this species.     

Mixed Spin-1/2 and Spin-5/2 Model by Renormalization Group Theory: Recursion Equations and Thermodynamic Study

Using the renormalization group approximation, specifically the Migdal-Kadanoff technique, we investigate the Blume-Capel model with mixed spins S = 1/2 and S = 5/2 on d-dimensional hypercubic lattice. The flow in the parameter space of the Hamiltonian and the thermodynamic functions are determined. The phase diagram of this model is plotted in the (anisotropy, temperature) plane for both cases d = 2 and d = 3 in which the system exhibits the first and second order phase transitions and critical end-points. The associated fixed points are drawn up in a table, and by linearizing the transformation at the vicinity of these points, we determine the critical exponents for d = 2 and d = 3. We have also presented a variation of the free energy derivative at the vicinity of the first and second order transitions. Finally, this work is completed by a discussion and comparison with other approximation.     

The Phase Diagram of the System [Ph4P]Br/BiBr3. Synthesis,Crystal Structure,Thermal Behaviour,and Vibrational Spectra of [Ph4P]3[Bi2Br9] · CH3COCH3 and two Modifications of [Ph4P]4[Bi6Br22]

The phase diagram of the system [Ph₄P]Br/BiBr₃ was investigated with the aid of DSC, TG and temperature dependent X‐ray powder diffraction measurements. By varying the reaction conditions, stoichiometry and crystallisation conditions of the reaction between BiBr₃ and [Ph₄P]Br four polynuclear bromobismuthates are formed. We report here the crystal structure of the solvation product [Ph₄P]₃[Bi₂Br₉] · CH₃COCH₃, which crystallises with monoclinic symmetry in the S. G. P2₁/n No. 14, a = 12.341(1), b = 32.005(3), c = 19.929(3) Å, β = 99.75(2)°, V = 7758(7) ų, Z = 4 and the crystal structures of two modifications of the compound [Ph₄P]₄[Bi₆Br₂₂]. The α‐form, crystallises with triclinic symmetry in the S. G. P1 No. 2, a = 13.507(4) Å, b = 14.434(4) Å, c = 17.709(5) Å, α = 81.34(2)°, β = 72.42(2)°, γ = 72.53(2)°, V = 3132.7(1) ų, Z = 2. The high‐temperature β‐form, crystallises with triclinic symmetry in the S. G. P1 No. 2, a = 13.893(4) Å, b = 14.267(3) Å, c = 16.580(3), α = 100.13(2)°, β = 96.56(2)°, γ = 110.01(2)°, V = 2985.5(1) ų, Z = 2. Lattice parameters of [Ph₄P]₄[Bi₈Br₂₈] are also given. The thermal behaviour of the compounds and in addition the vibrational spectra of [Ph₄P]₃[Bi₂Br₉] · CH₃COCH₃ are presented and discussed.     

Synthesis and Thermal Behaviour of Compounds in the System [Ph4P]Cl/BiCl3 and the Crystal Structures of [Ph4P]3[Bi2Cl9] · 2 CH2Cl2 and [Ph4P]2[Bi2Cl8] · 2 CH3COCH3

Six polynuclear chlorobismuthates are formed in the reaction between BiCl₃ and Ph₄PCl by variation of the molar ratio of the educts, the solvents and the crystallisation methods: [Ph₄P]₃[Bi₂Cl₉] · 2 CH₂Cl₂, [Ph₄P]₃[Bi₂Cl₉] · CH₃COCH₃, [Ph₄P]₂[Bi₂Cl₈] · 2 CH₃COCH₃, [Ph₄P]₄[Bi₄Cl₁₆] · 3 CH₃CN, [Ph₄P]₄[Bi₆Cl₂₂], and [Ph₄P]₄[Bi₈Cl₂₈]. We report the crystal structure of [Ph₄P]₃[Bi₂Cl₉] · 2 CH₂Cl₂ which crystallises with triclinic symmetry in the S. G. P1 No. 2, with the lattice parameters a = 13.080(3) Å, b = 14.369(3) Å, c = 21.397(4) Å, α = 96.83(1)°, β = 95.96(1)°, γ = 95.94(2)°, V = 3943.9(1) ų, Z = 2. The anion is formed from two face‐sharing BiCl₆‐octahedra. [Ph₄P]₂[Bi₂Cl₈] · 2 CH₃COCH₃ crystallises with monoclinic symmetry in the S. G. P2₁/n, No. 14, with the lattice parameters a = 14.045(5) Å, b = 12.921(4) Å, c = 17.098(3) Å, β = 111.10(2)°, V = 2894.8(2) ų, Z = 2. The anion is a bi‐octahedron of two square‐pyramids, joined by a common edge. The octahedral coordination is achieved with two acetone ligands. [Ph₄P]₄[Bi₄Cl₁₆] · 3 CH₃CN crystallises in the triclinic S. G., P1, No. 2, with the lattice parameters a = 14.245(9) Å, b = 17.318(6) Å, c = 24.475(8) Å, α = 104.66(3)°, β = 95.93(3)°, γ = 106.90(4)°, V = 5486(4) ų, Z = 2. Two Bi₂Cl₈ dimers in syn‐position form the cubic anion. Lattice parameters of [Ph₄P]₃[Bi₂Cl₉] · CH₃COCH₃ are also given. The solvated compounds are desolvated at approximately 100 °C. [Ph₄P]₃[Bi₂Cl₉] · 2 CH₂Cl₂ and [Ph₄P]₃[Bi₂Cl₉] · CH₃COCH₃ show the same sequence of phase transitions after desolvation. All compounds melt into a liquid in which some order is observed and transform on cooling into the glassy state.     

3,3′‐Dimesityl‐7‐methyl‐9a‐phenyl‐4,4′,5,5′,6,8,9,9a‐octa­hydro‐7H‐1,2,4‐oxa­diazo­lo­[4,5‐d][1,4]­diazepine‐8‐spiro‐5′‐isoxazole

Condensation of mesito­nitrile oxide with 1,7‐di­methyl‐5‐phenyl‐2,3‐di­hydro‐1H‐1,4‐diazepine leads to two cycloadducts (I) and (II). The structure and stereochemistry of the dicyclo­adduct (II) was established by X‐ray crystallographic analysis.