Etude de la fragmentation de derives de L'uracile et de la thymine par Spectrometrie de masse

Original mass spectra of uracil and thymine derivatives are presented with the corresponding fragmentation schemes. In the first series of spectra, the fragmentations of thymine derivatives, including ¹⁴C-2-thymine, dimers, and bromo thymines, confirm the basic retro Diels-Alder mechanism. The second series includes dihydro 5,6-derivatives of uracil (hydroxy and bromo substituents). The behaviour of these molecules is quite different; they are more sensitive to the substituents and a part of the fragmentation is often explained by protonated molecular ions.     

Influence de l'Insaturation Δ20(22) sur la Fragmentation du Cycle D des Stéroides

The mass spectra of two series of Δ20(22) unsaturated steroids have been studied. The analysis of the D-ring fragmentation shows that C-15? C-16 bond rupture is characteristic of the presence of this unsaturated sidechain.     

Spectrométrie de Masse de Benzylidène—Acétals d'Hexopyranosides

The electron impact fragmentation is reported for 46 benzylidene acetals of hexopyranosides of the allo, altro, galacto, gluco, gulo and manno series and some of their mono-oxidation products. Besides the molecular ion, which is always present and is usually part of a triplet the previously reported ion formed by cleavage of C-1? C-2, C-4? C-5 and the benzylic C? O(C-4) bond is observed. Evidence is given for two complementary ruptures (C-1? C-2, C-3? C-4; C-1? O-5, C-2? C-3, fragmentations whose intensities depend on the substituents or functional groups present in the molecule. In most cases these fragmentations allow an assignment of the substitution mode of these 1,3,6-trioxa-bicyclo-[4.4.0]decane systems. The limitations of this method are discussed.     

Etude de la reaction chlorocarbene-acetals de cetenes : II. Stereoselectivite de la reaction

We have studied the stereoselectivity of the addition reaction of chloro and chloromethyl carbenoids with ketene alkylsilyl acetals. The best stereoselectivity was generally observed with the dimethyl tertiobutylsilyloxy group. With the chlorocarbenoid, using an E ketene acetal we obtained in majority (8?0%) an E α,β-ethylenic ester and using a Z ketene acetal we obtained in majority (7?0%) a Z α,β-ethylenic ester. In the case of the chloromethyl carbenoid the two ketene acetal isomers led to the same E α-substituted α,β-ethylenic ester (8?8% of selectivity). With the chlorophenylcarbenoid, formation of 9?0% of E α phenyl α,β-ethylenic ester is observed.     

Structure de la rubranine, chalcone isolee de l'Aniba rosaeodora ducke

Rubranine, C₂₅H₂₆O₄ is a chalcone isolated from Aniba rosaeodora DUCKE. It has been established that its structure results from the condensation of a C-10 unit with 2,4,6-trihydroxychalcone.     

Recherches en série azabenzodiazépine. VI—etude en spectrométrie de masse de pyrazolo [3,4-b]diazépines-1,4

The mass spectra of 21 1,4-pyrazolo[3,4-b]diazepines are reported and analysed. Each of the five structures of the diazepine ring present is characterized by a particular group of fragmentations; among them one is common to all the compounds under study: the cleavage of C-5? C-6 and C-7? N-8 bonds leading to pyrazoloimidazoles ions.     

Etude en Basse Tension de l'Androstane Dione-3,17—Application a la Localisation du Deuterium

The fragmentation mechanisms of (5α) 3,17-androstanedione have been studied in order to determine whether the deuterium is located at C-4 or C-6. This is possible at low voltage where a peak at m/e 216, arising from a A-ring cleavage allows the determination of isotope distribution between C-4 and C-6.     

Influence de la temperature et du gradient de vitesse sur la viscosite des solutions diluees de xanthane

The dependence of the relative viscosity of a dilute xanthan solution (0.4 g·l^?1) has been studied as a function of temperature (20–70°) and of the ionic strength of the solvent. When the rate of shear exceeds 100 sec^?1, the viscosity can be expressed as γ̊ the exponent (n ? 1) varies with the polymer conformation. In aqueous solution in the absence or in the presence of added salt at a temperature above the melting temperature T_M (depending on the ionic strength of the solvent), the exponent (n ? 1) is ?0.285 and corresponds to the unordered conformation; at temperatures below T_M, the local helical conformation is rigid and (n ? 1) is ～ ?0.44 almost independent of the temperature.     

Etude expérimentale et théorique de la photolyse de dérivés du cycle pyrazolone

When irradiated in protic solvents such as water and primary alcohols, pyrazolinone derivatives undergo photocleavage between the two nitrogen atoms. Substituting the C-4 atom with an electronegative group stabilizes the open chain which is obtained but a thermal transposition takes place from the linear intermediate when C-4 carries a hydrogen atom or a methyl group. The $\text{STO}\text{3G}$abinitio scheme was used to study the photocleavage and the influence of the C-4 substituent, giving evidence of a mechanism which involves triplet excited states of the π, σ^* type.     

Synthese D'Azotures et de Benzoates de Glycosyle a Partir de Sulfites Cycliques Enc C-1, C-2

The reaction of sugars bearing a cyclic sulfite group on C-1, C-2 with azide or benzoate ions, is strereoselective and gives trans- 1,2 glycosyl azides or glycosyl benzoates with a free hydroxyle at C-2. The reaction is performed under mild conditions and gives excellent yields of glycosyl derivatives.     

Utilisation du calcul des modes normaux de vibration pour la détermination de la conformation de la glycylglycine et de la triglycine en solution aqueuse

The valence force field of α-glycylglycine was applied to different G matrices calculated for several values of the dihedral angles ψ₁, φ₂ and ψ₂. The relations v_i = ?(ψ_i,φ_i) obtained for different isotopic species were compared with the experimental frequencies of the aqueous solution thereby giving the absolute value of the angles. A complementary study by means of depolarised light scattering led to the determination of their sign. These relations were then used in the conformational analysis of triglycine in aqueous solution. The conformation of glycylglycine differs strongly in aqueous solution from that in the solid state, especially concerning the relative positions of the peptide and carboxylic group (φ₂ = ?70° and ?160°). For triglycine, we showed the existence of a chelated ring “C₇” similar to that observed for the acetylated dipeptides.     

Études en série indolique—XI : Synthèses dans la série de la dihydro-18, 19-dl antirhine

Three methods for the synthesis of (dl) 18, 19-dihydroantirhine and its epimers at C-15 and C-20 have been compared; a modified Polonovski reaction, mercuric acetate oxidation of the appropriate N-alkylpiperidine, and hydrogenation according to Wenkert of the appropriate pyridinium salt.     

Utilisation du 13C en Spectrométrie de Masse: Etude de la Fragmentation de Disaccharides

Twenty-nine α,β-(1 → 3) and (1 → 4) or β-(1 → 6) disaccharides, in the glucose series were analysed by electron impact mass spectrometry. In addition to the known mechanism, a few ¹³C labelled compounds led us to suggest that the ion c was formed from the reducing unit B and the C-1′ of the non-reducing residue A, while A was the starting point for rearrangement and fragmentation processes.     

Etude par RMN protonique d'heterocycles voisins de l'oxazaphospholane-1,3,2. II—Le diméthylamino-2 méthyl-3 oxazaarsolane-1,3,2

The ¹H NMR spectrum of the 2-dimethylamino-3-methyl 1,3,2 oxazaarsolane is very sensitive to solvent and temperature. A complete analysis of the spectrum at ?48 °C in deuteriated toluene shows that the molecule exists in a preferred conformation in the C-4? C-5 region. The spectrum, corresponding to an A₂X₂ system in nitrobenzene at +31 °C, indicates free movement around that bond. At higher temperatures a new coalescence phenomenon is explained by inversion of the As atom.     

Polymerisation cationique de l'indene amorcee par le tetrachlorure de titane-II Influence de la temperature sur la vitesse de polymerisation

Polymerization rates in the indene-titanium tetrachloride-methylene chloride system, using rigorously dried reagents, have been measured at various temperatures. At sufficiently high temperatures (above ?10°C), polymerization yields may be incomplete and cocatalytic phenomena have been observed; at low temperatures, yields are always complete. The reaction order in monomer is unity at ?70°C, which may be explained by a constant concentration of active centres during the major part of the reaction. At ?70°C, the reproducibility shows that residual water has no cocatalytic effect. The measured values of polymerization initial rates at various temperatures show that the apparent overall activation energy is negative. Various interpretations of this result are discussed, but it may be more easily reconciled with both the existence of a quasi-stationary state and an equilibrium between different types of active species.     

The mass spectrometry of 4-arylquinolizid-2-ones

The fragmentation pathways of ten 4-substituted quinolizid-2-ones were established using exact mass measurement, deuterium labelling and detection of metastable transitions. The base peak for most ketones was formed by cleavage of the C-2? C-3 bond (α to the carbonyl group) and the benzylic C-4? N bond. The decompositions examined were compared with those of the Nuphar alkaloids.     

Etude par RMN et uv de la protonation des enamines cationiques

Enamines, substituted on β carbon by a pyrylium cation have a mesomeric structure close to pyrannylidene—immonium. Conjugation between pyrylium nucleus and the double bond influences the relative stability of the C- and N- protonated compounds. This conjugation stabilizes the N-protonated compounds which are in equilibrium with the less conjugated C-protonated. In the same conditions, aliphatic enamines do not comprise such an equilibrium. The positions of the studied equilibria depend partly on the substituents of the β carbon and of the protonating reactant.     

Analyse Quantitative par Spectroscopie Infrarouge a Transformee de Fourier de la Partie Minerale de Charbons. Mise au Point et Application de la Technique

Abstract

Nous reportons dans ce mémoire des résultats ?analyses quantitatives de la matière minérale de charbon du bassin minier de Gardanne (France) par spectroscopie infrarouge a Transformée de Fourier.

Les cendres basse température (LTA) sont analysées par soustractions successives de spectres de minéraux de référence prealablement identifiés par diffraction X.

Une étude préliminaire sur des mélanges de minéraux purs est présentée. Le problème de ?échantillonage et du broyage est clairement posé et montre les possibilités et les limites de la technique IRTF. ?utilisation de minéraux locaux (Argiles grises et dolomite/calcite) permet ?étude des divers sites ?exploitation du bassin de Gardanne.

Cette étude préliminaire permet ?envisager une étude plus complète du site de Gardanne et sera mise en relation avec les procédés de combustion à basse température qui favorisent un piegeage partiel du SO₂ sous forme de sulfate.

We report in this work quantitative analysis results concerning mineral matter in Gardanne coals (France) using FTIR spectroscopy. The low temperature ashes (LTA) are analysed by successive spectral substractions of reference minerals which are before identified by X-ray diffraction.

A preliminary study of several mineral mixtures is reported.

The importance of the samples preparation and of the grinding is clearly shown as the possibilities and the limits of the FTIR method.

The use of local minerals (clays, calcite/dolomite) allow us to analyse various LTA samples of Gardanne coals.

These preliminary results will be useful for a further study of Gardanne coal basin in relation with low temperature combustion process involving partial trapping of SO₂ as sulfate.     

Reduction electrochimique des sulfures de fer application a la mesure de la non stoechiometrie

Iron sulfides Fe_1?xS are electrochemically reduced in chloride medium, at pH=0.2 according to a dissolution process. The coulometric measurement of the Fe(III) amount in the solid and the evaluation of the Fe²⁺ concentration in the solution after electroreduction lead to the determination of the stoechiometry on an amount of solid lower than one milligramme.     

Hétérocycles contenant du phosphore: XXVIII—Etude par Résonance Magnétique Nucléaire et analyse conformationnelle de quelques oxazaphosphorinanes-1,3,2 (II)

The ¹H n.m.r. spectra of some new 1,3,2-oxazaphosphorinanes are analysed. The stereochemistry and the ring conformation is discussed. The free energy and the torsional angle of the C-4? C-5 and C-5? C-6 fragments are calculated for some of these 1,3,2-oxazaphosphorinanes.