Mécanismes de Fragmentation en Spectrométrie de Masse par Ionisation Chimique. V–Echanges d'Atomes d'Hydrogène dans les Ions ‘aldehyde protoné’ à Longue Chaine Linéaire

Two different mechanisms for the loss of water from protonated long chain alkyl aldehydes, formed by chemical ionization, have been detected. The first involves a hydrogen exchange between the hydrogen bonded to the oxygen and those of the alkyl chain. This exchange is of lesser importance for aldehydes with less than six carbon atoms. A mechanism for this exchange is postulated. The second mechanism involves a transfer of a hydrogen atom, mainly from positions 3 and 4 of the alkyl chain, to the oxygen and subsequent loss of water.     

Effets Isotopiques dans la Fragmentation par Impact Électronique de Méthanols Deutériés

The mass spectra of the CH₃OH, CH₂DOH, CD₃OH, CH₃OD and CD₃OD methanols have been recorded at nominal electron energies ranging from 11 to 35 eV. Curves are given for the variation of the isotope effects related to the molecular ion stability and bond cleavage probabilities as a function of the electron energy, and are compared with a priori calculations. A simple distribution function and a value for the number of oscillators equal to half the theoretical figure give fairly satisfactory agreement, except as concerns the molecular ion stability. The form of the curves for the latter could be explained by the existence of an electronic state of the molecular ion other than the ground state.     

Méthode d''analyse par chromatographie liquide haute performance des formultions à base de mélanges d''acides phénoxycarboxyliques, de dicamba, d''ioxynil et de bromoxynil

High-performance liquid chromatography analysis of formulations of phenoxycarboxylic acids, dicamba, ioxynil and bromoxynil mixtures

Eighteen mixed formulations of phenoxycarboxylic acids and other herbicides such as dicamba, ioxynil and bromoxynil have been analyzed by high-performance liquid chromatography using a r-μm Nucleosil 50 column.

The concentration of acetic acid in the eluent hexane-acetic acid depends on the formulation to be analyzed and on the analysis time. The formulations are extracted with a chloroform-diethyl ether mixture, and 20 μ1 of the extract are injected onto the coloumn. The compounds are detected at 285 nm.

The method is simple, rapid and the formulations are specificially analyzed without derivatization.     

Méthode des Biorbitales: Application Préliminaire au Calcul de l'Energie de l'Etat Fondamental de l'Atome de Beryllium

The ground-state electronic energy of Be is calculated using the method of biorbitals (SCF –BI ). In this method the wave function is represented by an antisymmetrized product of identical pair functions. The basic set used to develop the biorbitals consists of the Watson s and p orbitals. The pair function is presumed to describe a singlet pair state. The energy associated with this function is minimized using a steepest descent procedure. A value of 0.0414 a.u. was found for the correlation energy, which is 44% of the total correlation energy. The SCF –BI method is compared with the CI method. The relationships are established between the expansion coefficients of both methods. The occupation numbers of orbitals are calculated.     

Formaldéhyde: calcul de l'énergie dans l'état fondamental par une méthode de perturbation

Résumé L'énergie électronique du formaldéhyde a été calculée ab initio dans une base minimale d'orbitales atomiques de Slater par la méthode de perturbation au deuxième ordre. On a utilisé des orbitales moléculaires S.C.F. symétriques et localisées et des orbitales moléculaires de liaison non S.C.F. La valeur finale de l'énergie varie assez peu avec le point de départ. L'emploi d'orbitales localisées permet d'interpréter les différentes contributions et de sélectionner les plus grandes.

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Formaldehyde: Ground state energy calculation by a perturbation technique

An ab initio calculation of the formaldehyde electronic energy is carried out by a second-order perturbation method, starting with a minimum basis set of Slater type atomic orbitals. Symmetry-adapted and localized S.C.F. molecular orbitals and non-S.C.F. bond orbitals are used. The total energy does not depend very much on the starting molecular orbitals. Localized orbitals lead to find out the largest contributions to the second-order energy and to interpret the various terms.

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Zusammenfassung Eine ab-initio-Rechnung der Elektronenenergie des Formaldehyd wurde mit einer Störungsrechnung zweiter Ordnung durchgeführt, dabei wurde mit einer minimalen STO-Basis begonnen. Es wurden lokalisierte SCF-Symmetrieorbitale und nicht bindende nicht SCF-Orbitale benutzt. Die Gesamtenergie hÄngt nicht sehr stark von den Ausgangs-MO's ab. Lokalisierte Orbitale ermöglichen es, die grö\ten EnergiebeitrÄge der zweiten Ordnung zu erhalten und die verschiedenen Terme zu analysieren.

     

Mécanismes de fragmentation en spectrométrie de masse par ionisation chimique. III—ions formés par cyclisation

Chemical ionization mass spectrometry of bifunctional organic molecules can induce fragmentation involving the formation of cyclic ions.     

Détermination de constantes de stabilité de chélates par résonance magnétique nucléaire du proton

In a solution containing an excess of two metal ions in regard to a ligand (e.g. NTA) a competitive equilibrium is established. The measure, by proton NMR. spectroscopy, of the individual concentrations of both chelates, and eventually of the free ligand, allows to determine the ratio of the stability constants of the two complexes. As an illustration the ratios of the stability constant of the 1:1 nitrilotriacetate chelates of Pb and Zn, respectively Mo and W, were determined.     

Le dosage de traces de cuivre dans l'arsenic tres pur par activation neutronique

The determination of traces of copper (<p.p.m.) in arsenic is impossible by non-destructive γ-spectrometry because of the similarity in the half-lives and spectra of the two isotopes used. The proposed separation and decontamination of copper are based on the following operations: bromine attack, hydrolysis, precipitation of barium arsenate, anion exchange, separation of copper as sulfide and recovery by electrolysis. Amounts of copper in the range 20–100 ng can be determined.     

Etude par Résonance Magnétique Nucléaire de dérivés phosphores. Etude de dithiaphospholanes-1,3,2

The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two ³J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the ³J(HH) values, the torsion about the C₄—C₅ bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.     

Résonance magnétique nucléaire du noyau 14N par Transformée de Fourier

¹⁴N-NMR. measurements using the Fourier Transform technique are presented and compared to C. W. experiments. The F. T. technique is especially advantageous for relaxation time measurements. However, since ¹⁴N-nuclei may have widely different relaxation times, it is often not possible to have optimal gain in sensitivity (as compared to C. W. measurements) in a single F. T. experiment for different ¹⁴N-nuclei contained in the same sample. Different experiments have to be performed, optimizing the spectrometer parameters for each ¹⁴N-resonance of appreciably different linewidth. The technique is applied to three different problems. ¹⁴N-relaxation in symmetrical ammonium salts is shown to arise from reorientation of the water dipoles. The use of a double spin-probe, ¹³C-¹⁴N, allows the determination of the electric field gradients in cyclic ammonium salts. The electronic distribution is especially distorted from tetrahedral symmetry in the highly strained N, N-dimethyl-aziridinium cation. Finally, electric and dynamic effects in ion pairing may be studied as shown on the case of tetrabutylammonium iodide in water and in benzene.     

Etude par RMN du Proton et du Carbone-13 de Pyrimidines Substituées. I—Effets de Substituant dans les Dérivés Méthylés et Aminés

Substituent effects of methyl and amino groups on the chemical shifts of pyrimidine have been investigated by ¹H and ¹³C n.m.r. and compared with similar data obtained for benzene and pyridine. Taking into account pairwise interactions, the chemical shifts calculated by using an additivity relationship are in very good agreement with the experimental results, except for some hindered pyrimidines. This study enabled us to assign the ¹³C n.m.r. spectra of some trisubstituted pyrimidines.     

Nouvelle méthode de détermination des taux de réativité des copolymères par résonance magnétique nucléaire: Application aux poly(méthacrylate de méthyle–chlorure de vinylidène)

Constant-composition copolymers of methyl methacrylate and vinylidene chloride produced by radical copolymerization are studied by ¹H-NMR at 60 and 250 MHz. The different methods of the literature for the derivation of reactivity ratios from either the copolymer composition or the sequence average lengths, or even the diad distribution, are applied but lead to rather dispersed results. A new graphical method is proposed, based on the use of peculiar values of the triad distribution functions. It allows us to detect a penultimate effect for the vinylidene chloride-rich region. In the same range, a change in tacticity of the diads and triads on the methylmethacrylate sequences, as compared with homopolymers, is observed; it suggests that the anomaly is caused by the competition of the depropagation reaction.     

Observations par microscopie électronique de traces d'ions lourds dans le triacétate de cellulose

Tracks of heavy charged particles have been observed in cellulose acetate by conventional electron microscopy (100 kV) and by high voltage microscopy (1, 2 MV). The tracks are formed of successive islets following each other at distances of 70-150 Å. With the evolution of the diameter of these zones is shown the existence of a highly perturbed cylindrical volume (diameter 400 Å for the case of krypton) corresponding to regions in which free radicals have been created. The different techniques used do not allow observation of the latent track because of the complications of energetic phenomena: the electron beam current density being limited, the contrast is small and hence the resolution is restricted.     

Etude par Résonance Magnétique Nucléaire de la thiamine (vitamine B1). Site de protonation-équilibre de tautomérie

Calculations are presented as evidence for the existence of a tautomeric equilibrium in thiamine and its polyphosphoric esters. The relative position of the equilibrium in these compounds is considered. Most of the experimental observations can be explained by the results of the calculations.     

Sur une méthode générale de synthèse des pyridones-2 condensées

Condensed 2-pyridones have been prepared by thermal cyclization of vinyl isocyanates substituted in β-position with aromatic heterocyclic radicals.     

Le dosage de traces d'argent dans le zinc extra-pur par activation neutronique

Below the p.p.m. level, the determination of silver in zinc by non-destructive γ-spectrometry is no longer feasible due to the activation of the matrix element. The activated zinc is dissolved in nitric acid, sulfamic acid and silver carrier are added, and ^110mAg (253 d) is obtained in a radiochemically pure state after two successive electrolyses on gold cathodes.After two days of irradiation in a thermal neutron flux of the order of 3.10¹³ n/cm²/sec (BR₂-Mol), 30 ng of silver can easily be evaluated with an error of 5%. Data obtained by integral γ-counting or by γ-spectrometry are compared.