Cinetique de polymerisation du styrene en presence de peroxyde de benzoyle p,p′ bis-bromomethyle synthese de polymeres peroxydes

The free radical polymerization of styrene has been studied by using p,p′-bisbromomethyl benzoyl peroxide as initiator containing a chain transfer group. The rate constant of decomposition (k_d) of this peroxide has been determined at various temperatures, as well as the efficiency factor f and the transfer constant to initiator C₁. At 60°, f = 0·70 ± 0·05 and C₁ = 0·5. Polystyrene containing peroxide groups has been prepared by using this initiator. The highest yield in polymeric peroxide has been obtained for polymerization in emulsion at 40°.     

The first synthesis of ent-agelasine F

Agelasine F has previously been isolated from marine sponges (Agelas sp.) and has been associated with various bioactivities including inhibitory activity on Mycobacterium tuberculosis. No total synthesis of this natural product has been reported. ent-Agelasine F has now been synthesized for the first time, starting from (R)-pulegone. The synthesis is considerably more efficient than a previously reported route to rac-agelasine F. ent-Agelasine F is found to exhibit antimicrobial activity.     

The nπ* states of the thiocarbonyl halides: The ā3A ← X̄1A' electronic transition in thiocarbonyl chlorofluoride

The visible absorption spectrum of thiocarbonyl chlorofluoride, C1FCS in the 495-nm region has been observed in the vapour phase under conditions of high resolution and pressure x path-length and has been assigned to the ā³A'' (n, π^*) ← X?¹A' electronic transition. Three of the six fundamental modes have been assigned for the upper electronic state. Prom a fit of the observed levels in v¹_o (the out-of-plane wagging mode) to the eigenvalues obtained from a quadratic-gaussian potential, the barrier to inversion in the ā³A state has been evaluated to be 1622 cm^?1 The electronic effects of replacing a sulphur by an oxygen atom on the height of the barrier to inversion in the nπ^* carbonyl and thiocarbonyl halides have been explored by the CNDO/2 method. The much lower barriers in the thiocarbonyl compounds has been attributed to the sulphur d_xz AO which is not present in the carbonyl compounds. This AO, which has relatively high weight in the LCAOs which form the π^* MO, has the effect of relieving some of the antibonding density which resides on the carbon atom and thereby reduces the barrier to inversion.     

Rydberg and autoionization tm states investigation by the three-step laser excitation and electric field ionization method

The energies of 190 Rydberg and autoionization 4f ¹³ 6snp-states of the Tm atom (ground electron configuration 4f ¹³ 6s ², nuclear chargeZ=69) have been measured by the laser multistep excitation with subsequent electric field ionization method. The investigation range of these states has been extended towards states with higher and lower values of the principal quantum number. As a result the energies of 160 states have been obtained for the first time. The experiment has been carried out on an automated laser photoionization spectrometer. The measurement accuracy has been ±0.5 cm^?1.     

The studies of molecular structure of Poly(1-trimethylsilyl-1-propyne) stereoisomers by the flow birefringence method

Optical properties of poly-1-trimethylsilyl-1-propyne (PTMSP) stereoisomers in solutions have been studied by means of flow birefringence method. Stereoisomers were chosen with various trans- and cis-configurations abundances of double CC bonds in monomeric units. The differences of main polarizabilities (α₁ − α₂) or statistical segments have been determined. Significant growth of (α₁ − α₂) values with increasing of the trans-isomer contents in chain molecule has been found. Optical anisotropy of monomeric segments, having cis- and trans-configurations, has been theoretically evaluated. It has been shown that observed significant increase of experimentally measured (α₁ − α₂) values cannot be sufficiently explained by only specific chain polarizability growth due to higher trans-isomers contents. It has been demonstrated that high (α₁ − α₂) value and it’s growth with increase of abundance of monomeric segments in trans-configuration has been caused by thermodynamical rigidity increase, i.e., higher number of monomeric units included into PTMSP statistical segment.     

Electronic structure of C40 possible structures

C₄₀ is a fullerene with a conformation that has been proposed as T_d, D_2d, D_4h and D_5d symmetry groups. The correct structure has not been determined because it has not been possible to isolate the molecule, but there have been several studies of minor fullerenes that include it. In this work we present a theoretical study at the gaussian 94 HF/3-21G level that gives answers about the principal differences between the mentioned structures and the possible thermodynamic stability of each one. Furthermore, we include a similar study on the new D_2h structure that we propose.     

Alignment of atomic autoionizing states created by slow Na++He collisions

Ejected-electron spectra have been measured for collisions of He-atoms with Na⁺-ions, whose impact energy ranged from 1.7 to 7.0 keV. The ion impact-energy dependence of the angular-differential cross-section of the ejected electrons has been investigated for an aligned autoionizing state Na**(2p ⁵ 3s ^{2 2} P), which has been created by charge transfer from the He-atoms. The alignment of the autoionizing state Na**(2p ⁵ 3s ^{2 2} P) is discussed in relation to the scattering angles of the Na⁺-ions. A complete longitudinal alignment has been observed with respect to the quasimolecular axis.     

On the Use of Monolithic Sol–Gel Derived Mesoporous Silica for the Calibration of Thermoporisemetry Using Various Solvents

Sol–gel derived mesoporous monolithic silica gels have been prepared to be used as standard materials for thermoporosimetry. The technique has been calibrated with n-heptane and cyclohexane and R _p = f(Δt) and W _a = f(ΔT) expressions are derived. In the specific case of cyclohexane, the solid to solid phase transition has been used. It is also shown that porous volumes can be measured by thermoporosimetry and that the correlation with N₂ gas sorption results is very good. Finally, thermoporosimetry has been applied to the study of cross linking level in polyisoprene samples containing a gradient of cross linking agent.     

Prediction of permselectivity of nitrate and acetate ions in the electrodialysis of aqueous solutions

Electrodialysis of aqueous solutions of acetic and nitric acids encountered in the industrial practice of deacidification of raw glyoxal solutions has been carried out to investigate the permselectivity of the system. The dependence of the permselectivity coefficient τ on experimental parameters such as flow velocity (V), current density (I), concentration of anions (C_i), etc. has been evaluated. A correlation between τ and the critical parameters has been obtained. Well-known theoretical equations have been used to calculate τ at limiting current density I_lim and as I approaches zero. Calculated results are compared with observed values. Limitations of theoretical procedures when applied to a system containing a weak acid are explained.     

Chemoenzymatic synthesis of calcilytic agent NPS-2143 employing a lipase-mediated resolution protocol

The kinetic resolution of chlorohydrin (±)-6 has been successfully carried out via a lipase-mediated transesterification with vinyl acetate in organic as well as ionic liquid media to yield (R)-alcohol 6 and (S)-acetate 7 in high enantioselectivity. An enantioconvergent synthesis has also been achieved by a Mitsunobu esterification of a mixture of (R)-alcohol 6 and (S)-acetate 7 in one pot to convert the (R)-alcohol 6 to (S)-acetate 7. (S)-Acetate 7 has been hydrolyzed by LiOH·H₂O to give epoxide (R)-2. This enantiopure epoxide has been used as a chiral precursor for the synthesis of calcilytic agent NPS-2143.     

Conductivity behaviour of proton conducting polymer gel electrolytes with PVdF-HFP

Electrical conductivity of polymer gel electrolytes containing different hydroxy substituted benzoic acids and polyvinylidenefluoride-hexafluoropropylene (PVdF-HFP) has been studied. The conductivity of solution and gel electrolytes shows ortho effect and has been found to depend upon the acidity constant of the acid used and varies as σ (ortho-) > σ (meta-) > σ (para-). The addition of PVdF-HFP to solution electrolytes results in an increase in conductivity and the conductivity of gel electrolytes has been found to be higher than that of the corresponding liquid electrolytes for all the three acids studied i.e. σ (gel) >σ (liquid). The increase in conductivity with polymer addition has also been found to depend upon the acid concentration.     

Molecular-dynamics simulation of the structural stability,energetics, and melting of Cu n(n = 13–135) clusters

Cluster properties of copper have been investigated using the Molecular-Dynamics md technique. The structural stability and energetics of spherical Cu_n (n = 13–135) clusters have been investigated at temperatures T = 1 K and T = 300 K. It has been found that the average interaction energy per atom in the cluster decreases and reaches an asymptotic value as cluster size increases. The melting behaviour of clusters n = 13 and n = 55 have been investigated. It has been found that the melting temperature decreases as cluster size increases, and for clusters with multishell structures melting starts from the outermost shell. In the simulation an emprical potential energy function (PEF) proposed by Erkoç has been used, which contains two-body atomic interactions.     

Synthesis and transport studies of new enantiopure lipophilic crown ethers containing a diarylphosphinic acid unit

The synthesis of new enantiopure lipophilic crown ethers (S,S)-6, (R,R)-6 and (S,S)-7 containing a diarylphosphinic acid unit has been carried out. The transport ability of these ligands has been studied in an aqueous source phase/lipophilic organic bulk liquid membrane/aqueous receiving phase system controlled by the pH of the media. The transport of metal ions and amines has also been studied. These studies showed high selectivity for protonated amines.     

Diode laser i.r. spectrum and rovibrational analysis of CF3Br in the ν2 + ν3 region

The gas phase i.r. spectrum of CF₃Br, with natural isotopic abundance, has been investigated in the ν₂+ ν₃ region near 1120 cm⁻¹ using a tunable diode laser spectrometer. The measurements have been carried out at low temperature (⋍ 200 K) to minimize the effects due to the “hot” band absorptions. The K structure of many P(J) and R(J) manifolds has been resolved and analyzed: the maximum J value reached for individual lines was 62 and 70 for CF₃⁷⁹Br and CF₃⁸¹Br, respectively. The identified transitions have been used in a least-squares fit to the energy expression up to the quartic terms and molecular parameters for the ν₂ + ν₃ combination have been obtained. Residual weak features due to “hot” bands of ν₃ and ν₆ have been assigned; the J structure has been analyzed by means of a polynomial procedure and spectroscopic constants for both the isotopomers have been derived.     

Vibrational spectra,methyl torsional potential functions,internal rotational potential functions,and conformational properties of ethyl vinyl ether

The vibrational spectra of ethyl vinyl ether in both the fluid and solid states have been recorded from 20 to 3500 cm^?1. The 33 fundamental modes of vibration have been assigned. Three rotational isomers have been observed and their structures have been determined. The most stable conformer, s-cis/s-trans, is planar and of C_s symmetry. The two less stable rotamers, skew/s-trans and skew/gauche, are non-planar and of C_i molecular symmetry. The barrier to internal rotation of the methyl rotor has been determined for each conformation; these barriers are 3.43 kcal mol^?1 (s-cis/s-trans), 3.35 kcal mol^?1 (skew/s-trans) and 3.19 kcal mol^?1 (skew/gauche). A potential function for each of the two asymmetric internal rotations has been calculated and barriers to conformer interconversion have been determined. From the asymmetric potential function calculations, ΔH, the enthalpy difference between the conformers, has been determined. The s-cis/s-trans conformer is 1.87 kcal mol^?1 more stable than the skew/s-trans conformer; the skew/s-trans conformer is more stable than the skew/gauche conformer by 1.10 kcal mol^?1. The energetics of conformer interconversion and methyl internal rotation have been described in terms of molecular geometry and non-bonded interactions. These results are compared to those found in other alkyl vinyl and dialkyl ethers.     

Diferric oxo-bridged complexes of a polydentate aminopyridyl ligand: synthesis,structure and catalytic reactivity

The catalytic reactivity of a group of diferric oxo-bridged complexes (1–3) of a tetradentate ligand (bpmen = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-1,2-diaminoethane) toward alkane hydroxylation has been evaluated. Among the three complexes, the µ-oxo diiron(III) complex [Fe(bpmen)(µ-O)FeCl₃] (1) has been synthesized for the first time. The complex 1 has been characterized by spectroscopic analysis and X-ray crystallography. At room temperature, the µ-oxo diiron(III) complexes 1–3 have been found to be useful catalysts in hydroxylation of alkanes with m-chloroperbenzoic acid as oxidant. [Fe(bpmen)(µ-O)FeCl₃] (1) has been found to be the most active catalyst. Moreover, the catalytic ability of the complexes in the oxidation of alcohols to ketones with hydrogen peroxide at room temperature has also been investigated.     

Standard enthalpy of formation of fluorinated graphite CF0.96

The energy of combustion ?? _c U ⁰ of fluorinated graphite CF_0.96 has been determined using an isoperibolic calorimeter with a rotating platinized bomb and the enthalpy of formation ?? _f H ⁰ thereof has been calculated. The enthalpy of the dissociation of the C-F bond has been calculated from the obtained value of ?? _f H⁰(CF_0.96) and compared with analogous values for the previously investigated C₆₀ fullerene fluorides.     

Manifestation of steric factors in electrode kinetics: Investigations of the deposition and dissolution kinetics of the Cd2+/Cd(Hg) system in presence of adsorbed aliphatic alcohols and acids

The role of the steric factors in the electrode reactions occurring on the interface covered by aliphatic alcohols and acids has been investigated, taking as an example the Cd²⁺/Cd(Hg) system. It has been shown that this process takes place inside the inner layer and the activated complex is created by the replacement of r^≠ water molecules from the surface. From studies carried out at surfactant concentrations corresponding to the plateau of the adsorption isotherm the steric factors r^≠/r_i have been determined (r_i is the number of solvent molecules replaced from the surface by one molecule of adsorbed surfactant). By comparison with investigations performed at lower coverages the magnitude of r^≠ and r_i has been estimated. The influence of different factors on the experimental value of these parameters has been discussed.     

Crystalline structure and OH torsional motion in calcium-strontium arsenate apatites

The crystalline structure of Ca_10?xSr_x(AsO₄)₆(OH)₂ has been studied, and the lattice parameters determined. It has been found that the unit cell expands with x. Geometric parameters of the unit cell, which are defined in relation to the hindered rotation of the OH group around the c axis, have been also obtained. From the ir data, the torsional potential function has been calculated in first and second approximations. A method for computing that function in any order approximation is given. A semiempirical curve is found, relating the stretching and torsional motions for both the OH and OD groups.     

Structural and electrical conductivity studies of Li x AlZr[PO4]3 (x = 1.8, 2.0, 2.2), solid electrolyte for lithium-rechargeable batteries

In the present study, Li _x AlZr[PO₄]₃ (x = 1.8, 2.0, 2.2) has been prepared by the Pechini-type polymerizable precursor method, and structural and electrical analyses have been performed. Formation of the compound has been confirmed from X-ray diffraction pattern. Vibrational analysis has been performed using Fourier transform infrared spectroscopy. Ion transport mechanism has been analyzed using the AC impedance technique. Electrical characterization reveals that the maximum conductivity (4.4 × 10^?5S cm^?1) has been observed for the sample Li_2.2AlZr[PO₄]₃ at 673K.