Etude théorique de derives substitués du benzène

Résumé Dans les conditions explicitées lors du premier article de cette série, la méthode semi-empirique de Pariser-Parr-Pople est appliquée à l'étude électronique des dialcoxybenzènes symétriques. Le calcul met en évidence l'influence de la position relative des substituants sur les potentiels d'ionisation, le déplacement des bandes électroniques du benzène et les intensités des bandes d'absorption. Pour les dérivés ortho et para, ce travail met en évidence l'existence d'un transfert électronique lors de l'excitation jusqu'aux deux premiers singulets excités, alors qu'un phénomène analogue se produit pour les quatre premiers singulets des composés méta. Enfin la réactivité chimique des positions substituables de ces molécules est discutée.

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Theoretical study of substituted benzenesII. Symmetrical dialkoxybenzenes

In the conditions we gave in the first paper, the semi empirical Pariser-Parr-Pople's method has been applied for the electronic study of symetrical dialkoxybenzenes. These calculations show the effect of the substituants position on ionization potentials, spectroscopic shifts on benzene absorption bands and corresponding intensities. This work indicates that the excitation to the first and second singlet induces an electronic transfer from the heteroatom in the case of ortho and para derivatives; for meta compounds, the same phenomenon occurs for the four first singlets. At last, the reactivity of substituable positions is discussed.

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Zusammenfassung Die im Teil I erfolgte Untersuchung der Monoalkoxybenzole wurde auf die entsprechenden Dialkoxyverbindungen ausgedehnt, wobei sich zeigt, wie Ionisierungspotentiale, Absorptions- und IntensitÄtsverschiebungen von der gegenseitigen Lage der Substituenten abhÄngen. Die ersten zwei SingulettübergÄnge zeigen im Fall der ortho- und para-Verbindungen Ladungsübergang; im Fall der meta-Verbindungen sind es die ersten vier.

     

Surface plasmon near-field imaging of very thin microstructured polymer layers

We report on the near-field imaging of microstructured polymer layers deposited on an homogeneous metal thin film on which a surface plasmon mode is excited. The microstructures in the polymer layers are designed by electron beam lithography, and the near-field imaging is performed with a photon scanning tunneling microscope (PSTM). We show that, despite their very small height, the microstructures can be conveniently imaged with a PSTM thanks to the field enhancement at the surface of the metal thin film supporting the surface plasmon. The influence of the illumination conditions on the contrast of the PSTM images is discussed. In particular, we show that both the field enhancement and the near-field intensity distribution around the microstructures depend dramatically upon the illumination conditions, leading to the conclusion that the PSTM is well suited for spatially resolved near-field surface plasmon sensing purposes.     

Identification by Electron Probe Microbeam Analysis of Submicron Borides in Joints of Nickel Base Superalloys

The phases formed at the interface between an intermetallic (NiAl) and a nickel base superalloy joined by combustion synthesis were investigated, particularly the eutectic phases. Owing to their small size, the characterisation of these phases using a Castaings electron microprobe encounters difficulties. The analysis volume size is generally too large to differentiate the phases from their surrounding matrix, even by using low accelerating voltage. Moreover, the eutectic phases contain boron, which is difficult to characterise by EPMA. Independently of the phases shape, the characterisation can be solved by viewing this complex system as a surrounding matrix and a multi layer system. The results of these simulations revealed the presence of two categories of borides: the eutectic boride MM₂B₂ (M=Mo and M=Co, Cr) and the solid solution boride [Cr_1–x (Mo, W)_x]B.     

Preparation et caracterisation des polymeres tete-a-tete—VI. Proprietes physicochimiques du polystyrene tete-a-tete en solution diluee. Comparaison avec des polystyrenes de structure differente

The dilute solution properties of head-to-head polystyrene are reported. Determination of the “θ” temperature in cyclohexane has been made and compared with the “θ” temperature of the head-to-tail polystyrene (polyprotostyrene and poly-deuteriostyrene). The viscometric behaviour in a good solvent has been also examined and compared with the properties of head-to-tail polystyrenes (atactic, isotactic and deuterated).     

Antiferromagnetic three-dimensional order induced by carboxylate bridges in a two-dimensional network of [Cu3(dcp)2(H2O)4] trimers

A new Cu(II) complex, [Cu(3)(dcp)(2)(H(2)O)(4)](n), with the ligand 3,5-pyrazoledicarboxylic acid monohydrate (H(3)dcp) has been prepared by hydrothermal synthesis, and it crystallizes in the monoclinic space group P2(1)/c with a = 11.633(2) A, b = 9.6005(14) A, c = 6.9230(17) A, beta = 106.01(2) degrees, and Z = 2. In the solid state structure of [Cu(3)(dcp)(2)(H(2)O)(4)](n), trinuclear [Cu(3)(dcp)(2)(H(2)O)(4)] repeating units in which two dcp(3-) ligands chelate the three Cu(II) ions with the central Cu(II) ion, Cu(1) (on an inversion center), link to form infinite 2D sheets via syn-anti equatorial-equatorial carboxylate bridges between Cu(2) atoms in adjacent trimers. These layers are further linked by syn-anti axial-equatorial carboxylate bridging between Cu(1) atoms in adjacent sheets resulting in the formation of a crystallographic 3D network. A detailed analysis of the magnetic properties of [Cu(3)(dcp)(2)(H(2)O)(4)](n) reveals that the dcp(3-) ligand acts to link Cu(II) centers in three different ways with coupling constants orders of magnitude apart in value. In the high temperature region above 50 K, the dominant interaction is strongly antiferromagnetic (J/k(B) = -32 K) within the trimer units mediated by the pyrazolate bridges. Below 20 K, the trimer motif can be modeled as an S = 1/2 unit. These units are coupled to their neighbors by a ferromagnetic interaction mediated by the syn-anti equatorial-equatorial carboxylate bridge. This interaction has been estimated at J(2D)/k(B) = +2.8 K on the basis of a 2D square lattice Heisenberg model. Finally, below 3.2 K a weak antiferromagnetic coupling (J(3D)/k(B) = -0.1 K) which is mediated by the syn-anti axial-equatorial carboxylate bridges between the 2D layers becomes relevant to describe the magnetic (T, H) phase diagram of this material.     

Gas chromatographic/mass spectrometric determination of 3-methoxy-1,2-propanediol and cyclic diglycerols, by-products of technical glycerol, in wine: interlaboratory study

The aim of the present study was to provide the official wine control authorities with an internationally validated method for the determination of 3-methoxy-1,2-propanediol (3-MPD) and cyclic diglycerols (CycDs)-both of which are recognized as impurities of technical glycerol-in different types of wine. Because glycerol gives a sweet flavor to wine and contributes to its full-body taste, an economic incentive is to add glycerol to a wine to mask its poor quality. Furthermore, it is known that glycerol, depending on whether it is produced from triglycerides or petrochemicals, may contain considerable amounts of 3-MPD in the first case or CycDs in the second. However, because these compounds are not natural wine components, it is possible to detect glycerol added to wine illegally by determining the above-mentioned by-products. To this end, one of the published methods was adopted, modified, and tested in a collaborative study. The method is based on gas chromatographic/mass spectrometric analysis of diethyl ether extracts after salting out with potassium carbonate. The interlaboratory study for the determination of 3-MPD and CycDs in wine was performed in 11 laboratories in 4 countries. Wine samples were prepared and sent to participants as 5 blind duplicate test materials and 1 single test material. The concentrations covered ranges of 0.1-0.8 mg/L for 3-MPD and 0.5-1.5 mg/L for CycDs. The precision of the method was within the range predicted by the Horwitz equation. HORRAT values obtained for 3-MPD ranged from 0.8 to 1.7, and those obtained for CycDs ranged from 0.9 to 1.3. Average recoveries were 104 and 109%, respectively.     

Mesoionic compounds VIII. Synthesis of 3-phenylsydnonyl substituted alkenes. Some new photochromic sydnones

The reactions of 3-phenylsydnonyllithium with a variety of ketones to afford tertiary carbinols 4a-4i and their subsequent dehydration to 4-(3-phenylsydnonyl) alkenes 5a-5i are discussed. Among the alkenes, 2-[4-(3-phenylsydnonyl)]propene ( 5b ) and 1-[4-(3-phenylsydnonyl)]-1-cyclohexene ( 5i ) were photochromic. A Wittig reaction between ethyl-4-(3-phenylsydnonyl)-ketone and methylenetriphenylphosphorane afforded the photochromic 2-[4-(3-phenylsydnon-yl)]-1-butene(5j).     

Electroorganic synthesis. Reductive alkylation of functionalized 1,2-dithiole-3-thiones

Two-electron reduction of some substituted 1,2-dithiole-3-thiones 1 followed by alkylation of the dianionic intermediates leads through electrosynthesis to mixture of Z and E isomers of the corresponding substituted alkyl-(3-thioalkyl)-2-propenedithioates 2, 3 in satisfactory yield. The structure of those products was established by ¹³C and ¹H nmr and mass spectroscopy. The isomers ratios were determined by nmr spectroscopy.     

Fluorescence spectroscopy for monitoring deterioration of extra virgin olive oil during heating

The potential of fluorescence spectroscopy for characterizing the deterioration of extra virgin olive oil (EVOO) during heating was investigated. Two commercial EVOO were analysed by HPLC to determine changes in EVOO vitamin E and polyphenols as a result of heating at 170°C for 3 h. This thermal oxidation of EVOO caused an exponential decrease in hydroxytyrosol and vitamin E (R²=0.90 and 0.93, respectively) whereas the tyrosol content was relatively stable. At the same time, amounts of preformed hydroperoxides (ROOH), analysed by an indirect colorimetric method, decreased exponentially during the heating process (R²=0.94), as a result of their degradation into secondary peroxidation products. Fluorescence excitation spectra with emission at 330 and 450 nm were recorded to monitor polyphenols and vitamin E evolution and ROOH degradation, respectively. Partial least-squares calibration models were built to predict these indicators of EVOO quality from oil fluorescence spectra. A global approach was then proposed to monitor the heat charge from the overall fluorescence fingerprint. Different data pretreatment methods were tested. This study indicates that fluorescence spectroscopy is a promising, rapid, and cost-effective approach for evaluating the quality of heat-treated EVOO, and is an alternative to time-consuming conventional analyses. In future work, calibration models will be developed using a wide range of EVOO samples.