Sterically Facilitated Intramolecular Nucleophilic NMe2 Group Substitution in the Synthesis of Fused Isoxazoles: Theoretical Study

The influence of steric repulsion between the NMe₂ group and a second ortho-(peri-)substituent in the series of 1-dimethylaminonaphthalene and N,N-dimethylanilene ortho-oximes on the ease of the NMe₂ group’s intramolecular nucleophilic substitution is studied. Possible reaction intermediates for three mechanisms are calculated (ωB97xd/def-2-TZVP), and their free Gibbs energies are compared to model reaction profiles. Supporting experiments have proved the absence of studied reactivity in the case of simple 2-dimethylaminobenzaldoxime, which allowed us to establish reactivity limits. The significant facilitation of NMe₂ group displacement in the presence of bulky substituents is demonstrated. The possibility of fused isoxazoles synthesis via the intramolecular nucleophilic substitution of a protonated NMe₂ group in the aniline and naphthalene series is predicted.     

Transition-metal bimaleates and their solid solutions: Synthesis,structural, and thermoanalytical study

Transition-metal hydrogen maleates of composition M(C₄H₃O₄)₂ · 4H₂O, where M = Mn, Fe, Co, and Ni, and their solid solutions were synthesized and characterized by X-ray crystallography, IR spectroscopy, mass spectrometry, and thermal analysis. X-ray crystallography and IR spectroscopy showed that both intramolecular and intermolecular H-bonds exist in these compounds. The generation of continuous substitutional solid solutions with cation substitution in these compounds was studied. The thermolysis mechanism was studied for both transition-metal hydrogen maleates and their solid solutions. The composite produced by thermolysis is stable up to 1200°C in flowing helium.     

Photodynamics of polyene-polymethine transformations and spectral fluorescent properties of merocyanine dyes

Absorption and fluorescence spectrum band moments (center of gravity, width, asymmetry, excess, and fine structure) have been determined in a wide range of solvents with different polarities for inverse solvatochromic di-, tetra-, and hexamethinemerocyanines derived from 1,3-diphenyl-2,3-dihydro-1H-benzimidazole. Juxtaposition of the quantum-chemically calculated (by the semiempirical AM1 method) charges, bond orders, and dipole moments of the merocyanine molecules in the ground and excited singlet states with the experimentally observed spectral fluorescent characteristics suggests that the molecular electronic structure in the two states can vary from a nonpolar polyene via a polymethine to a charge-separated polyene, depending on the length of the polymethine chain and the medium polarity. As shown, solvatofluorochromism gives rise to smaller spectral band shifts than those of solvatochromism. This effect is attributable to weaker intermolecular solute-solvent interactions in the fluorescent excited state due to the more equalized charges as compared to those of the ground state. A lack of mirror symmetry of the absorption and fluorescence spectra has been revealed for di- and tetramethinemerocyanines (broadened fluorescence bands) as well as for hexamethinemerocyanines (narrowed fluorescence bands); the two cases are accounted for by the different behavior of vibronic and intermolecular interactions in the course of absorption and emission. As found for merocyanines, the electronic structure of their fluorescent state approaches the cyanine limit and the ground state becomes increasingly polyene-like with lengthening of the polymethine chain. A close vicinity of the excited state to the cyanine limit causes a dramatic increase in fluorescence quantum yields and a decrease in Stokes shifts observed for higher merocyanine vinylogues.     

Incomplete averaging effects in the ESR spectra of randomly oriented paramagnetic particles

Experimental studies on a Fe³⁺-natrolite model system were performed to investigate formatiom of noiselike magnetic resonance spectra previously found in polycrystalline zeolite samples and some other finely divided systems. The results of these studies show that the observed noiselike spectra are nonaveraged sets of lines from randomly oriented microcrystals. Physical conditions of formation of noiselike spectra are formulated, and methods to extract previously inaccessible information are proposed.     

One-dimensional model of inhomogeneous shear in sliding

The paper briefly describes a one-dimensional dynamic model of plastic shear deformation in a material surface layer in sliding friction, giving grounds to the reduction of the problem dimension from 3D to 1D. A selection of simulation results is presented to illustrate the peculiarities of plastic deformation under the action of two competitive processes — work hardening and thermal softening due to frictional heating. Presented also are experimental data on which to base the conclusion on the possibility of surface layer flow similar to flow of a viscous fluid. To assess from the Reynolds number whether turbulization of the surface layer is feasible, simulation results are used.     

Magnetocaloric effect and multifunctional properties of Ni–Mn-based Heusler alloys

The studies of magnetocaloric properties, phase transitions, and phenomena related to magnetic heterogeneity in the vicinity of the martensitic transition (MT) in Ni–Mn–In and Ni–Mn–Ga off-stoichiometric Heusler alloys are summarized. The crystal structure, magnetocaloric effect (MCE), and magnetotransport properties were studied for the following alloys: Ni₅₀Mn_50−xIn_x, Ni_50−xCo_xMn₃₅In₁₅, Ni₅₀Mn_35−xCo_xIn₁₅, Ni₅₀Mn₃₅In₁₄Z (Z=Al, Ge), Ni₅₀Mn₃₅In_15−xSi_x, Ni_50−xCo_xMn_25+yGa_25−y, and Ni_50–xCo_xMn_32−yFeyGa₁₈. It was found that the magnetic entropy change, ΔS, associated with the inverse MCE in the vicinity of the temperature of the magneto-structural transition, TM, persists in a range of (125-5) J/(kg K) for a magnetic field change ΔH=5 T. The corresponding temperature varies with composition from 143 to 400 K. The MT in Ni₅₀Mn_50−xIn_x (x=13.5) results in a transition between two paramagnetic states. Associated with the paramagnetic austenite-paramagnetic martensite transition ΔS=24 J/(kg K) was detected for ΔH=5 T at T=350 K. The variation in composition of Ni₂MnGa can drastically change the magnetic state of the martensitic phase below and in the vicinity of TM. The presence of the martensitic phase with magnetic moment much smaller than that in the austenitic phase above TM leads to the large inverse MCE in the Ni₄₂Co₈Mn_32−yFeyGa₁₈ system. The adiabatic change of temperature (ΔT_ad) in the vicinity of TC and TM of Ni₅₀Mn₃₅In₁₅ and Ni₅₀Mn₃₅In₁₄Z (Z=Al, Ge) was found to be ΔT_ad=−2 K and 2 K for ΔH=1.8 T, respectively. It was observed that |ΔT_ad|≈1 K for ΔH=1 T for both types of transitions. The results on resistivity, magnetoresistance, Hall resistivity in some In-based alloys are discussed.     

Chemoselective hydrogenation of 3-nitrostyrene over Ag/TiO2-SiO2 catalyst in a flow reactor

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Fluorescence modulation of eosin Y in a PMMA film by diarylethene switching

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