Sterically congested ‘roofed’ 2-thiazolines as new chiral ligands for copper(II)-catalyzed asymmetric Diels-Alder reactions

Newly introduced chiral ‘roofed’ 2-thiazolines, prepared from sterically congested, conformationally rigid chiral 2-aminothiols, function as efficient chiral ligands for the asymmetric Diels-Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone.     

Chronopotentiometry at very small stationary disk electrodes

Expressions for chronopotentiometry at very small stationary disk electrodes are presented. The transition time, τ, is expressed as a function of I_ss/I, where I is the applied current and I_ss is the steady-state diffusion current for the disk electrode given by I_ss/I=4nFc*_RDa, (where n is the number of electrons transferred, a the radius of the electrode, D the diffusion coefficient and c*_R the bulk concentration). When values of I_ss/I are small, the transition time constant,

, depends linearly on I_ss/I and gives the intercept of the Sand equation. When I_ss/I approaches unity, the transition time increases rapidly and diverges to infinity at I_ss/I=1. If I_ss/I exceeds unity, the transition does not occur and the electrode potential approaches a steady-state value corresponding to I. An approximate equation for the transition time is presented, from which one can evaluate the diffusion coefficient. Equations for the potential-time curve and the quarter-wave potential are also obtained. The equations were tested experimentally using platinum small disk electrodes (a=0.025–0.10 mm). The transition times obtained experimentally were in good agreement with these predicted theoretically for various values of the applied current, for several different radii of the electrodes.     

Physicochemical properties and structures of room temperature ionic liquids. 2. Variation of alkyl chain length in imidazolium cation

The alkyl chain length of 1-alkyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([Rmim][(CF(3)SO(2))(2)N], R = methyl (m), ethyl (e), butyl (b), hexyl (C(6)), and octyl (C(8))) was varied to prepare a series of room-temperature ionic liquids (RTILs), and the thermal behavior, density, viscosity, self-diffusion coefficients of the cation and anion, and ionic conductivity were measured over a wide temperature range. The self-diffusion coefficient, viscosity, ionic conductivity, and molar conductivity change with temperature following the Vogel-Fulcher-Tamman equation, and the density shows a linear decrease. The pulsed-field-gradient spin-echo NMR method reveals a higher self-diffusion coefficient for the cation compared to that for the anion over a wide temperature range, even if the cationic radius is larger than that of the anion. The summation of the cationic and anionic diffusion coefficients for the RTILs follows the order [emim][(CF(3)SO(2))(2)N] > [mmim][(CF(3)SO(2))(2)N] > [bmim][(CF(3)SO(2))(2)N] > [C(6)mim][(CF(3)SO(2))(2)N] > [C(8)mim][(CF(3)SO(2))(2)N], which greatly contrasts to the viscosity data. The ratio of molar conductivity obtained from impedance measurements to that calculated by the ionic diffusivity using the Nernst-Einstein equation quantifies the active ions contributing to ionic conduction in the diffusion components, in other words, ionicity of the ionic liquids. The ratio decreases with increasing number of carbon atoms in the alkyl chain. Finally, a balance between the electrostatic and induction forces has been discussed in terms of the main contribution factor in determining the physicochemical properties.     

Mathematical modelling of the superplastic forming of a long rectangular sheet

Standard finite element software (ANSYS FEM-code) is used to model the superplastic forming of a superplastic sheet alloy into a rectangular die. As distinct from other known approaches the boundary value problem is stated in the present study in terms of the theory of creep. The results of finite element calculations are found to be in a good agreement with corresponding analytical solutions and experimental data for titanium sheet alloy Ti-6Al-4V. The approach suggested can be used in practice for estimating the current geometry and the thickness of the dome and the time intervals both for the constant gas pressure forming and for the constant strain rate forming.     

Cyclization of 1,4-dines in an rf plasma,an apparent di-π-methane rearrangement

1,4-Pentadiene reacted when flowed through a 13.6 MHz gaseous discharge forming vinylcyclopropane, cyclopentene and cyclopentadiene; 3-phenylpropene reacted similarly producing cyclopropylbenzene and indene.     

A phenomenological analysis on γp → π+n, πOp below 1.2 GeV

A phenomenological partial-wave analysis on γp → π⁺n and π^Op reactions has been performed in the energy range 0.25–1.2 GeV with available data, laying special emphasis on the polarization and asymmetry data. A good fit has been obtained.     

Characterization of the adsorption state of carbonate ions at the Au(111) electrode surface using in situ IRAS

The spectro-electrochemical behavior of carbonate and bicarbonate ions at the Au(111) electrode surface was studied using the infrared reflection absorption spectroscopy (IRAS). An absorption band caused by the adsorbed carbonate ions was observed in the wavenumber region of 1425–1511 cm⁻¹ both in Na₂CO₃ and NaHCO₃ solutions. It was concluded that the adsorbed carbonate ions co-ordinate with the electrode surface in the unidentate state with their symmetry axis normal to the substrate. This orientation is retained in the whole potential region where carbonate ions adsorb on the electrode surface in contrast to the behavior of the carbonate ions adsorbed on the Pt(111) electrode surface.     

Surrogate analysis for detecting nonlinear dynamics in normal vowels.

Normal vowels are known to have irregularities in the pitch-to-pitch variation which is quite important for speech signals to be perceived as natural human sound. Such pitch-to-pitch variation of vowels is studied in the light of nonlinear dynamics. For the analysis, five normal vowels recorded from three male and two female subjects are exploited, where the vowel signals are shown to have normal levels of the pitch-to-pitch variation. First, by the false nearest-neighbor analysis, nonlinear dynamics of the vowels are shown to be well analyzed by using a relatively low-dimensional reconstructing dimension of 4 < or = d < or = 7. Then, we further studied nonlinear dynamics of the vowels by spike-and-wave surrogate analysis. The results imply that there exists nonlinear dynamical correlation between one pitch-waveform pattern to another in the vowel signals. On the basis of the analysis results, applicability of the nonlinear prediction technique to vowel synthesis is discussed.     

Polarized target asymmetry in π+ photoproduction between 0.3 and 1.0 GeV at 130°

The polarized target asymmetry in the reaction γp → π⁺n has been measured at c.m. angles around 130° for photon energies between 0.3 and 1.0 GeV by detecting the π⁺ only. The asymmetry is compared with recent analyses.     

Mechanism of diffusion and sorption of carbon dioxide in poly(vinyl acetate) above and below the glass transition temperature

The pressure dependence below 1 atm of the apparent diffusion and permeation coefficients were observed by using the permeation time lag method for carbon dioxide in poly(vinyl acetate), which has a glass transition near room temperature, at temperatures ranging from 8 to 50°C. Above the glass transition temperature, pressure dependence of the diffusion and permeation coefficient has not been observed; hence, Fick's law with a concentration independent diffusion coefficient applies. On the other hand, in the glassy state, the apparent diffusion coefficient shows pressure dependence. Moreover, the behavior of the pressure dependence does not show a clear curve in the ranges between 30°C to 17°C. Above 17°C, the apparent diffusion coefficients show discontinuities, but below 17°C increase with pressure is regular. Using the theoretical prediction of Paul, a computer was used in the numerical calculation to determine the true diffusion coefficient and other dual sorption parameters. p]The compensated diffusion coefficients controlled only by Henry's law dissolution was described by three straight lines with two intersection in the form of Arrhenius plots, which give good agreement with both our results for He and Ar and those of Meares. It is assumed that beside the dual sorption mechanism, another effect, for instance some relaxation effect may also contribute to the diffusion for carbon dioxide in poly(vinyl acetate) near the glass transition temperature region.