Ozonolysis of a Series of Methylated Alkenes: Reaction Rate Coefficients and Gas‐Phase Products

The gas‐phase ozonolysis of three methylated alkenes, i.e., trans‐2,2‐dimethyl‐3‐hexene (22dM3H), trans‐2,5‐dimethyl‐3‐hexene (25dM3H), and 4‐methyl‐1‐pentene (4M1P), has been investigated in the presence of sufficient hydroxyl radical scavenger in a laminar flow reactor at ambient temperature (296 ± 2 K) and P = 1 atm of dry air (RH ≤ 5%). Ozone levels in the reactor were monitored by an automatic analyzer. Alkene and gas‐phase product concentrations were determined via online sampling either on three‐bed adsorbent cartridges followed by thermodesorption and GC/FID‐MS analysis or on 2,4‐dinitrophenylhydrazine (DNPH) cartridges for subsequent HPLC/UV analysis. Reaction rate coefficients of (3.38 ± 0.12) × 10^?17 for 22dM3H and (2.71 ± 0.26) × 10^?17 for 25dM3H, both in cm³ molecule^?1 s^?1 units, have been obtained under pseudo–first‐order conditions. Primary carbonyl products have been identified for the three investigated alkenes, and branching ratios are reported. In the case of 4M1P ozonolysis, the yield of a Criegee intermediate was indirectly determined. Kinetics and product study results are compared to those of literature when available. This work represents the first investigation of reaction products in the ozonolysis of 22dM3H, 25dM3H, and 4M1P in a flow reactor.     

Glass transitions and mixed phases in block SBS

Differential scanning calorimetry (DSC) does not allow for easy determination of the glass‐transition temperature (T_g) of the polystyrene (PS) block in styrene–butadiene–styrene (SBS) block copolymers. Modulated DSC (MDSC), which deconvolutes the standard DSC signal into reversing and nonreversing signals, was used to determine the (T_g) of both the polybutadiene (PB) and PS blocks in SBS. The T_g of the PB block was sharp, at ?92 °C, but that for the PS blocks was extremely broad, from ?60 to 125 °C with a maximum at 68 °C because of blending with PB. PS blocks were found only to exist in a mixed PS–PB phase. This concurred with the results from dynamic mechanical analysis. Annealing did not allow for a segregation of the PS blocks into a pure phase, but allowed for the segregation of the mixed phase into two mixed phases, one that was PB‐rich and the other that was PS‐rich. It is concluded that three phases coexist in SBS: PB, PB‐rich, and PS‐rich phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 276–279, 2005     

Domain decomposition for an asymptotic geological fault modeling

We present in this paper a domain decomposition method to treat faults in geological basin modeling. The particularity of this model is that the faults whose widths are very small in comparison with the basin size, are not characterized as subdomains any more but as interfaces between sedimentary blocks. The originality of this work lies in the formulation of this new fault model and in the definition and the computation of the interface conditions between the subdomains. To cite this article: E. Flauraud et al., C. R. Mecanique 331 (2003).     

Thermal and chemical nanofractal relaxation

We studied shape relaxation of nano-fractal islands, during annealing, after their growth from antimony cluster deposition on graphite surface. Annealing at 180^°C shows evidence of an increase of the fractal branch width with time followed by branch fragmentation, without changing the fractal dimension. The time evolution of the width of the arm suggests the surface self-diffusion mechanism as the main relaxation process. With Monte Carlo simulations, we confirmed the observed behavior. Comparison is done with our previous results on fragmentation of nano-fractal silver islands when impurity added to the incident cluster promotes rapid fragmentation by surface self-diffusion enhancement [1].     

Enhancement of mass spectrometric detection of LTC4, LTD4, and LTE4 by derivatization

Several acylating reagents are synthesized and used to introduce quatemary phosphonium or ammonium or ternary sulfonium functions into a simple model of a peptido leukotriene (PLT). One of these reagents was selected for further study with LTE₄, LTD₄, and LTC₄. We demonstrate that acylation of the free amine function of PLTs to produce the 5-triphenylphosphoniumvaleryl-amide (TPPV) derivatives enhances chemical stabilities and significantly increases responses in fast-atom bombardment and continuous-flow liquid secondary ion mass spectrometry (CF-LSIMS) relative to the native PLTs. With high-performance liquid chromatography inlet to CF-LSIMS, we demonstrate the facile detection in selected ion monitoring of the TPPV derivative of 3 pg of LTD₄.     

Synthesis of silver molybdate clusters driven by laser-annealing

The synthesis of silver rich molybdate clusters is achieved by laser induced chemical reaction of coadsorbed MoO(3) and O(2) molecules on free silver clusters. The reactants MoO(3) and/or O(2) molecules condensed at low temperature (77 K-175 K) on free silver clusters. Then, the silver clusters together with their adsorbed molecules are flashed either ionized with a discharge or ionized and heated by a laser. Then they are cooled down by evaporation. The synthesized chemical compounds are analyzed by a high-resolution time-of-flight mass spectrometer. If only one type of reactant is adsorbed on the cluster, only one oxide molecule is stabilized on the metallic core after the heating and cooling cycle. On the contrary, the coadsorption of the two types of molecules MoO(3) and O(2) on Ag(n) (+), at 77 K, leads to complex aggregates that transform, after laser heating, into a molybdate rich metal clusters. These synthesized species cool down by evaporating silver atoms showing evidence of a binary oxide that is more stable than the metallic core. Moreover we demonstrate that for small size molybdate clusters, a stoichiometric composition may differ from the bulk one.     

Syntheses and configurations of some heterocyclic amidoximes. X-Ray crystal structure of 3-phenyl-5,6-dihydro-2(1H)-pyrazinone-O-methyloxime

O-Methyl-α-ketophenylacetohydroximoyl chloride ( 1 ) was prepared by the reaction of O-methyl-α-methoxyphenylacetohydroximoyl chloride ( 5 ) with N-bromosuccinimide and concentrated hydrobromic acid. Reaction of 1 with ethylenediamine gave 3-phenyl-5,6-dihydro-2(1H)-pyrazinone-O-methyloxime ( 6 ). 3-Phenyl-5,6-cyclohexano-5,6-dihydro-2(1H)-pyrazininone-O-methyloxime ( 7 ) was prepared by reaction of 1 with trans-1,2-diaminocyclohexane. The X-ray structure of 6 has been determined. The crystals are orthorhombic, space group Pbca with a = 10.264(3), b = 18.262(4), c = 23.530(4)Å, V = 4411(2)ų, and Z = 16. The structure, which was refined to R = 0.038 using 1652 observed reflections, shows the amidoxime moiety to be the Z configuration. Reaction of benzohydroximoyl chloride with aziridine gave (Z)-aziridinylbenzaldoxime ( 16a ). Ultraviolet irradiation of a benzene solution of 16a gave a mixture of the Z and E isomers 16a and 16b . The E isomer 16b underwent thermal isomerization to 16a at 100°. Reaction of 16a with dimethyl sulfate in sodium hydroxide solution gave (Z)-O-methylaziridinylbenzaldoxime ( 17a ). Photoisomerization of a hexane solution of 17a gave a mixture of the Z and E isomers 17a and 17b which were separated by preparative glc. The isomers 17a and 17b are resistant to thermal Z = E isomerization. The mechanisms of thermal isomerization of benzamidoximes are discussed.     

Determination de la structure de perfluoroalcenes a chaines longues par R.M.N. du19F : lère Partie : pefluoroalcenes-1

After a review of 1-perfluoroalkene R_FCFCF₂ synthesis, with R_FC₄F₉, C₅F₁₁, C₆F₁₃, we have studied their fine structures by ¹⁹F N.M.R. This study has led us to first generalize the rules set for the chemical shifts and coupling constants of olefinic fluorine atoms of fluoropropene and their derivatives. Then, we have been able to determinate unambiguously the chemical shifts of the difluoromethylene groups of the perfluorinated chains. We have thus shown, by irradiation, that inversions may take place in the chemical shifts of the CF₂ groups at the β and γ position of the double bond.