Spectrometrie de Masse des Acetates de la Serie Bicyclo-(2.2.1) heptane. Elimination de Cetene et Fragmentation Type

Elimination of ketene is shown to occur through a four centre mechanism with the acetates of the bicyclo[2.2.1] series. A typical fragmentation, related to the rearrangements of carbonium ions, is induced by an unsaturation at position 3.     

Simultaneous analysis of polychlorinated biphenyls and organochlorine pesticides in water by headspace solid-phase microextraction with gas chromatography-tandem mass spectrometry

Headspace solid-phase microextraction combined with gas chromatography-ion trap tandem mass spectrometry (HS-SPME-GC-ITMS-MS) method has been developed and studied for the simultaneous determination of 15 organochlorine pesticides (OCPs) and 20 polychlorinated biphenyls (PCBs) in aqueous samples. To perform the HS-SPME polydimethylsiloxane (PDMS) (7, 30 and 100 microm film thickness) and polydimethylsiloxane-divinylbenzene (PDMS-DVB) fibers were initially compared on the basis of their absorption capacities for the selected compounds, and PDMS 100 microm film thickness was selected to accomplish the rests of essays. The influence of various parameters on OCPs and PCBs extraction efficiency by HS-SPME was thoroughly studied using GC-electron capture detector (ECD). Parameters such as collision induced dissociation (CID) resonant excitation amplitude and RF storage level were optimized to increase specificity and sensibility for ITMS-MS analysis. The performance of proposed HS-SPME-GC-ITMS-MS methodology with respect to linearity, reproducibility and limit of detection (LOD) was evaluated by water spiked with target compounds. The linear range of most compounds was found to be between 0.01 and 1 ng mL(-1) and the limits of detection were between 0.4 and 26 pg mL(-1). The reproducibility of the method (n = 6), expressed as relative standard deviation (RSD), was between 5 and 21%. Finally, developed procedure was applied to determine selected OCPs and PCBs in river water samples in concentration below 0.1 ng mL(-1) can be easily carried out with ultra-selectivity and precision.     

Photoreactivite de l'ester de dieckmann α-methyle. Applications de la reaction du type I de norrish a la synthese du dihydroterpenediol secrete par danaus chrysippus et a celle des alcools du lilas

The α-methyl Dieckmann ester, when irradiated with UV light, gives a mixture of relatively light stable E and Z isomers of 5-carbethoxyhex-4-en-1-al 2, (77% yield). Although the 2E isomer can be isolated in pure form in almost 50% yield, separation of the two isomers is unnecessary. Their formation has been used as a key step in the total synthesis of the dihydroterpenediol 3 (34% overall yield) secreted by Danaus Chrysippus (African Monarch), and the four lilac alcohols 4.     

Fragmentation des δ-Dicetones,Analogies Avec le Comportement Photochimique

The mass spectra of thirty δ-diketones are reported. Their main pathways have been rationalized with the aid of deuterium labelling, metastable ions and high resolution mass measurements. Special attention has been given to ions resulting from the expulsion of neutral molecules such as water preceded, or followed by the loss of ethylene or alkenes. The expulsion may involve an intermediate cyclobutanol ion which would be analogous to the photochemical reaction observed by Yang.     

Analysis of functionalized polyisobutylenes by capillary SFC, SEC, HPLC, and CGC-MS after fraction collection

Summary An analytical strategy has been developed for analysis of polyisobutylenes partially functionalized with isothiocyanate groups ( ) by capillary supercritical-fluid chromatography (CSFC), size- exclusion chromatography (SEC), and reversed-phase liquid chromatography (RPLC). Fractions collected from semi-preparative RPLC and SEC were further characterized by capillary GC-MS (gas chromatography coupled with mass spectrometry). Complete characterization of the polymer was achieved by comparing the results obtained from the different techniques. The degree of polymerization and the relative quantity of the different series of macromolecular chains of polyisobutylene were estimated.     

Gas-phase reactivity of the O=P(OCH3)2 + phosphonium ion towards alpha,beta-unsaturated esters in a quadrupole ion trap

Ion-molecule reactions between the O=P(OCH3)2 + phosphonium ions and eight alpha,beta-unsaturated esters (methyl acrylate, ethyl acrylate, methyl crotonate, ethyl crotonate, methyl 3,3-dimethylacrylate, ethyl 3,3-dimethylacrylate, methyl methacrylate and ethyl methacrylate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH3)2 + phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with alpha,beta-unsaturated esters to give an adduct [RR'C=CR'COOR', O=P(OCH3)2]+, which lose spontaneously a molecule of trimethyl phosphate (R'=CH3) or dimethyl ethyl phosphate (R'=C2H5). An ion corresponding to a protonated trialkyl phosphate is also observed when substituent R'=H. To confirm the experimental results, and to elucidate the mechanism for the formation of the ionic species, a theoretical study using the density functional theory (DFT) approach was carried out. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH3)2 + and methyl acrylate is described.     

Spatial reshaping of a squeezed state of light

Reshaping the spatial profile, or mode, of a quantum state of light is one of the challenges in many quantum optics applications. We test the noise properties of a universal programmable mode converter and demonstrate that it can reshape the spatial mode of a beam while retaining its quantum properties. No detectable amount of noise is added to the light and only the standard transmission losses through conventional optical elements are found to affect the non-classical nature of the transformed light.