Steric and Electronic Factors Influence Regio‐isomeric Thiazole Formations Between Substituted Benzothioamides and Ethyl Bromopyruvate

We observed unexpected thiazole 1B formation when 2,6‐dichlorobenzothioamide 1 and ethyl bromopyruvate were reacted under basic conditions at elevated temperatures in ethanol. Thiazole 1B , regio‐isomeric to that expected under conventional Hantzsch conditions, was extensively characterized and later confirmed by single crystal X‐ray structure. We carried out this transformation with several substituted benzothioamides and found that the formation of the unexpected thiazole regio‐isomer was highly dependent on the steric as well as the electronic characteristics of the ortho‐substituents on the phenyl ring. A mechanism to account for this novel transformation was proposed.     

Infrared dispersion of lead phosphate at room temperature

Infrared reflection spectra [15–4000 cm^-1] along the b (binary axis) and c axes (A_u and B_u-type modes) are reported at room temperature as obtained with a Fourier-transform scanning interferometer. The spectra are analyzed with the factorized form of the dielectric function and the infrared-active mode parameters are reported.     

Infrared dispersion of potassium zinc chloride

The infrared reflection spectra for the three main polarizations of K₂ZnCl₄ in the orthorhombic commensurate ferroelectric phase are reported at room temperature. Phonon frequencies are assigned to internal and external modes by comparison with K₂SeO₄ and Rb₂ZnCl₄ data. The dielectric constant along the ferroelectric axis is essentially due to the weight of the low-frequency heavily-damped mode.     

Infrared reflectivity analysis of perovskite ceramics Sr(Sr13Nb23)O3

The infrared reflection of polycrystalline samples of perovskite $\text{Sr(Sr}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)O}{}_3$ are reported and analysed with Kramers-Kronig inversion. Results give information on the structures of the high-temperature and low-temperature forms of the atomic arrangements.     

Diffusion phenomena of a cold gas in a thermal plasma stream

The present study involves both experimental investigation and mathematical modeling of the diffusion process of a cold gas injected into a main plasma stream. The cold gas (nitrogen or helium) was injected axially through a water cooled tube located along the centerline of an induction plasma torch. The 2-D distribution of the temperature, velocity and concentration profiles in the plasma flow were measured using enthalpy probe techniques. The results are compared with the predictions of a 2-D, LTE, turbulent mathematical model. The effects of the nature (composition) of the injected gas and its mass flow rate are investigated. The enthalpy probe measurements and the predictions of the model are in good agreement. The effective (turbulent and molecular) transport properties are estimated from a comparison of the measured and calculated profiles of the temperature, velocity and concentration fields. This study sheds light on the basic diffusion mechanisms involved in a widely used configuration of induction plasma reactors, i.e. in which the material to be treated is injected axially into the plasma, through a central water cooled tube.     

Operator coproduct-realization of quantum group transformations in two-dimensional gravity I

A simple connection between the universalR matrix ofU _q(sl(2)) (for spins 1/2 andJ) and the required form of the coproduct action of the Hilbert space generators of the quantum group symmetry is put forward. This leads us to an explicit operator realization of the coproduct action on the covariant operators. It allows us to derive the expected quantum group covariance of the fusion and braiding matrices, although it is of a new type: the generators depend upon worldsheet variables, and obey a new central extension of theU _q(sl(2)) algebra realized by (what we call) fixed point commutation relations. This is explained by showing on a general ground that the link between the algebra of field transformations and that of the coproduct generators is much weaker than previously thought. The central charges of our extendedU _q(sl(2)) algebra, which includes the Liouville zero-mode momentum in a non-trivial way, are related to Virasoro-descendants of unity. We also show how our approach can be used to derive the Hopf algebra structure of the extended quantum-group symmetry related to the presence of both of the screening charges of 2D gravity.Partially supported by the EC contracts CHRXCT920069 and CHRXCT920035.Unité Propre du Centre National de la Recherche Scientifique, associée à l'École Normale Supérieure et à l'Université de Paris-Sud.     

Intermediate steps in YBa2Cu3O7−x synthesis by sol-gel method: YBaCuO oxycarbonate

High T _c -superconducting powders of the Y-Ba-Cu-O system are prepared by a solution-polyacrylamide gel using citric acid as a complexing agent. This method provides an easy way to prepare reactive YBaCuO powders by sol-gel synthesis. However this synthesis involves intermediate phases formation which impedes the obtention of the pure phase at low temperature. An intermediate oxycarbonate phase forms between 800° and 850°C in flowing oxygen. From powder X-ray diffraction, thermal analysis and IR spectroscopy, it is concluded that the intermediate oxycarbonate has an average tetragonal structure—SG P4/mmm—similar to that of the parent oxide with a stoichiometry close to YBa₂Cu_2.95(CO₃)_0.35O_6.6. The carbonate group is located in the center of the basal CuO square. This compound has superconducting properties. A pure 123 phase is obtained when the xerogel precursor is annealed at 925°C in O₂ or at 800°C in Ar, then in O₂. The grain growth and microstructure development of YBaCuO have also been investigated and compared using two different powders, i.e. sol-gel route and commercial powder from Hoechst.     

Mixing study of the induction plasma reactor: Part I. Axial injection mode

A systematic study of the gas-mixing pattern in an induction plasma reactor under atmospheric and low pressure conditions is reported. Different reactor configurations were investigated in which nitrogen is injected as an auxiliary gas either axially into an Ar/H₂, discharge in the center of the induction coil region, or radially through multiple orifices, into the plasma jet at tire exit nozzle of the torch. Concentration mapping in the mixing zone was carried out, using a VG-Microniass-PC 300 D mass spectrometer at plasma power levels and reactor pressures, in the range of 13–24 k 6V and 35–93 kPa, respectively. Comparison of these results with cold-flow measurements underlined the substantial difference in the mixing pattern in each of these two cases. A considerably faster mixing of the gases is noted under cold flow conditions compared to that in the presence of the discharge. The results are discussed from the viewpoint of their use for optimum reactor design applied to tire vapor-phase synthesis of ultrafine ceramic powders, using induction plasma technology.     

Polymerization of substituted olefins initiated by organometallic compounds of titanium (IV)—II. Evidence for a predominant radical process with methyltitanium derivatives

Polymerizations of methyl methacrylate (MMA), vinyl acetate, acrylonitrile or styrene (St) initiated by methyl derivatives of Ti(IV) are consistent with a radical process. This conclusion is supported by tacticities of the resulting polymers which are close to those for conventional radical samples and show that propagation obeys a Bernoullian statistics. The major evidence is provided by statistical MMA-St copolymerization which clearly exhibits radical reactivity ratios.