Molecular structure and theoretical studies of new stable phosphorus ylides derived from trialkyl phosphites

The reaction between dialkyl acetylenedicarboxylates and NH heterocyclic compounds in the presence of trialkyl phosphite leads to stable phosphorus ylide derivatives in good yields. The x‐ray crystallographic data and theoretical study show that there is a resonance between two bonds of C₉P₁ and C₉₁O₉₁ in phosphorous ylide 4c . This compound crystallizes in the triclinic system, space group ( ), with the following unit cell parameters: a = 8.7522(3)Å, b = 8.8513(5)Å, c = 18.3469(5)Å, α = 99.1220(10)°, β = 90.954(2)°, γ = 118.792(2)°, Z = 2, and V = 1222.72(9)ų. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:36–43, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20653     

Synthesis of novel furo-pyran derivatives via reaction between an isocyanide and alkylidene-substituted Meldrum’s acid

An unexpected four-component (3+1) reaction of an alkyl isocyanide with alkylidene-substituted Meldrum’s acid in CH₂Cl₂ at room temperature produces imino-furopyranones in good yields. The structures of the products are deduced from their IR, ¹H NMR, and ¹³C NMR spectra and by X-ray analysis. The products are structurally similar to 2H-furo[2,3-c]pyran-2-one natural products.     

Development of eclipsed and staggered forms in some hydrogen bonded complexes

Intermolecular hydrogen bonding in X₃CH···NH₃ (X = H, F, Cl, and Br) complexes has been studied by B3LYP, B3PW91, MP2, MP3, MP4, and CCSD methods using 6‐311++G(d,p) and AUG‐cc‐PVTZ basis sets. These complexes could exist in both eclipsed (EC) and staggered (ST) forms. The differences between binding energies of EC and ST forms are negligible and all EC and ST shapes correspond to minimum stationary states. The order of stabilities of them is in an agreement with the results of atoms in molecules (AIM) and natural bond orbital (NBO) analyses. On the basis of low differences between binding energies, ST forms are more stable than EC forms in all complexes with the exception of Br₃CH···NH₃, which behaves just opposite. Although the differences between binding energies are negligible, they are consistent with the results of AIM analysis. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Mössbauer study and magnetic properties of Fe–Si–B–Cu amorphous systems with minor substitution of carbon

Journal of Radioanalytical and Nuclear Chemistry - The effect of minor substitution of carbon on the structure and magnetic properties of Fe–Si–B–Cu-type metallic glasses was...     

Stability assessment and operating parameter optimization on experimental results in very small plasma focus,using sensitivity analysis

Regarding the importance of stability in small-scale plasma focus devices for producing the repeatable and strength pinching, a sensitivity analysis approach has been used for applicability in design parameters optimization of an actually very low energy device (84 nF, 48 nH, 8–9.5 kV, ～2.7–3.7 J). To optimize the devices functional specification, four different coaxial electrode configurations have been studied, scanning an argon gas pressure range from 0.6 to 1.5 mbar via the charging voltage variation study from 8.3 to 9.3 kV. The strength and efficient pinching was observed for the tapered anode configuration, over an expanded operating pressure range of 0.6 to 1.5 mbar. The analysis results showed that the most sensitive of the pinch voltage was associated with $0.88\pm 0.8\text{mbar}$ argon gas pressure and 8.3–8.5 kV charging voltage, respectively, as the optimum operating parameters. From the viewpoint of stability assessment of the device, it was observed that the least variation in stable operation of the device was for a charging voltage range of 8.3 to 8.7 kV in an operating pressure range from 0.6 to 1.1 mbar.     

Estimates on the dimension of an exponential attractor for a delay differential equation

We study the long time behavior of delay differential equation, considered in a bounded domain in ? ^d . Using the short trajectory method to prove the existence of the exponential attractor. Also we have estimates on the fractal dimension of an exponential attractor.     

Thermal properties of undoped, S-doped, Nb-doped, and S, Nb co-doped titania nanoparticles prepared by sol–gel method

One of the classic methods to extend the spectral response of a wide band gap titania semiconductor to visible light is impurity doping. This study has studied undoped, S-doped, Nb-doped, and S, Nb co-doped titania nanopowders prepared by sol–gel. The relationship between the doping conditions and the thermal stability, phase composition, crystallinity, morphology of particles, and the influence of dopant in similar conditions was investigated. Also the relationship between the dopant and the properties of titania nanosized powders, such as thermal stability, phase composition, crystallinity, morphology and size of particles, was investigated. Thermogravimetry coupled with differential thermogravimetry, X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscope was used for the characterization of the materials. During heating of the air dried samples, their chemical degradation took place giving rise to anatase phase.     

Efficient Synthesis of Highly Functionalized,S -Alkyl 1-Alkyl-4,4-dimethyl-2,5-dioxo-pyrrolidine-3-carbothioates

5-Isopropylidene-2,2-dimethyl-1,3-dioxane-4,6-dione (the condensation product of Meldrum's acid and acetone) reacts with alkyl isocyanides in the presence of this to produce S -alkyl 1-alkyl-4,4-dimethyl-2,5-dioxo-pyridine-3-carbothioates in good yield.     

ZnO as an Effective and Reusable Heterogeneous Catalyst for the Synthesis of Arylaminotetrazoles

ZnO is an effective heterogeneous catalyst for the reaction between arylcyanamides with sodium azide to synthesize the arylaminotetrazoles in good yields. This method has advantages of good yields, simple methodology, short reaction times, and easy workup. Furthermore, the catalyst can subsequently be reused for several times without any significant loss of activity.     

UV spectrophotometric study of the kinetics and mechanism of the reactions between triphenylphosphine, dialkyl acetylenedicarboxylates and NH-acid

To determine the kinetic parameters of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of an NH-acid, such as 2,3-di-hydroxybenzaldehyde, the reactions were monitored by UV spectrophotometry. The second order fits were automatically drawn and the values of the second order rate constants (k₂) were calculated using standard equations as part of the program. The dependence of the second order rate constant (lnk₂) on the reciprocal temperature was in agreement with the Arrhenius equation, in the temperature range studied, providing the relevant plots to calculate the activation energy of all reactions. Furthermore, we evaluated the effects of solvent, structure of different alkyl groups within the dialkyl acetylenedicarboxylates, and their concentration on the rates of reactions. The proposed mechanism was confirmed by experimental results and steady-state approximation. The first step (k₂) of the reaction was recognized as the rate determining step on the basis of experimental data.