Mecanismes de la protonolyse des organo-chromiques issus de bromures propargyliques.

The reaction of CrCl₂ with propargylic bromides leads to an allenic organo—chromic derivative protonated without rearrangement by carboxylic acids. Alcohols like methol transform this metallic to its propargylic isomer and then protonate it with rearrngement (S_Ei′ type mechanism).     

Mecanismes de fragmentation pyrolytique du phenol et des cresols

The thermal cracking of phenol and ortho and para-cresol at atmospheric pressure, between 665°C and 865°C has been studied with a contact time of 2·5 seconds. ¹⁴C- and ³H-labelled substrates have been used in mechanistic studies of these processes. Elimination of one carbon monoxide produced quasi-exclusively by loss of the carbon of the hydroxyl function of the phenols is the first step and leads to the formation of cyclopentadiene or of a C₅H₆ compound. A condensation of two phenol molecules with loss of water and hydrogen to form dibenzofuran occurs simultaneously. The formation mechanism of this last compound is different according to the cracking temperatures.     

Fragmentation de derives phenyles de l'isobenzofuranne et de l'isoindole

The fragmentation patterns of two paris of heterocycil compounds are investigated in order to discuss the effect of the nature of the heteroatom.     

Fragmentation sous impact electronique de l'acetate de tertiobutyle

The mass spectral fragmentation of tert-butylacetate has been studied by means of high resolution studies, deuterium labelling and metastable transition determinations. Besides the McLafferty rearrangement, two less classical rearrangement mechanisms of oxygen-containing ions are observed and some isotope effects are reported.     

Mecanismes de durcissement structural des alliages plomb-cadmium (etain,argent) pour grilles de batterie I- alliages plomb-cadmium

The reequilibration of supersatured Pb-Cd alloys was studied by different experimental methods: hardness measurements, optical and electron microscopy, electron microprobe. Two structural states were considered: as-cast alloys, rehomogenised alloys. The Cd contents were 1, 1.5, 2 and 3.2 weight%. The explored temperatures were 20 and 80 °C. This last temperature corresponds to the curing temperature of battery's grids and to the highest operating temperature. The evolution of the quenched structure towards the equilibrium state was studied for the time range one minute to one year. The corresponding aging is characterized by a continuous precipitation and a discontinuous transformation. The hardening process is followed by an overaging which consists of a discontinuous transformation with a reprecipitation of the Cd from the fine hardening precipitates of the same phase.     

Etude de la Fragmentation de Derives Substitues Polycycliques du Benzodioxinne-1,4

The mass spectra of five polycyclic 1,4 benzodioxin derivatives have been studied. The breakdown patterns of the more important ions have been suggested by comparison with three compounds in a deuterated specific position. Some rearrangements are produced by specific hydrogen migration and a few others after scrambling.     

Isomerisation du Thiazole et de l'Isothiazole avant Fragmentation

The molecular ions of thiazole and isothiazole mainly isomerize to a common structure before fragmentation, as evidenced by the analysis of metastable ions abundances and kinetic energy releases.     

Fragmentation de Benzodioxannes-1,3 Diversement Substitues en 2,4

Under electron-impact, two ‘retro’ Diels-Alder fragmentation paths are observed in the spectra of 2,4- substituted 1,3-benzodioxan; one with normal ‘retro’ Diels-Alder reaction and the other with hydrogen transfer.     

Action des phenylacetonitriles α-substitues sur les tetrahalomethanes en milieu basique: Mecanismes de l'halogenation et de la duplication

Carbanions of substituted phenylacetonitriles are halogenated by carbon tetrachloride or carbon tetrabromide, and also converted into symmetrically-substituted succinonitriles. The halogenation occurs via an ionic process, and the formation of succinonitriles via a radical process, essentially a no-chain mechanism in the case of diphenylacetonitrile anion, confirmed by the course of the reaction of p-nitrobenzylchloride on the diphenylacetonitrile anion.     

Etude de la Fragmentation du Benzisothiazole et de Quelques Benzoselenazoles et Benzisoselenazoles

The mass spectra of benzisothiazole, three benzoselenazoles and three benzisoselenazoles have been determined and compared with those of the corresponding benzothiazoles. The elimination of CS known to occur from these latter substances is confirmed in the case of benzisothiazole, but a different mechanism is proposed. The fragmentation of the selenium analogues led to ions of the same type as the benzothiazoles and benzisothiazole, through extrusion of molecules of the type CN—R, but loss of the heteroatom was not accompanied by loss of carbon. Furthermore, the isoselenazole structure seems to be more sensitive to electronolysis than its isomer. All six selenium heterocyclics investigated gave rise to two ions (130 and 132) resulting from a recombination of various fragments, suggesting that this is a characteristic feature of the electron-impact fragmentation of compounds of this type.     

Spectrometrie de masse—VI. Fragmentation de dimethyl-2,2 dioxolannes-1,3 insatures

The mass spectral fragmentation behaviour of a series of unsaturated 2,2-dimethyl 1,3-dioxolanes has been determined from metastable ion evidence and high resolution mass spectrometry. Plausible rationalizations for the formation of the principle ion-fragments formed in their mass spectra are presented.     

Etude de la Fragmentation des bis Alkylthio-3,5 Isothiazoles en Spectrometrie de Masse

The study of the fragmentation schemes of twenty-six 3,5-Bis(alkylthio)-isothiazoles allows us to show new fragmentation modes in the isothiazole series. Two important breakdowns could be distinguished in the case of 3,5-Bis(alkylthio)-isothiazoles, from examination of the data concerning the spectra of the deuteriated derivatives in each position concerning the loss of the mer-capto radical and of two atoms of sulphur, respectively. We have shown the specific effect of the thio-alkyl substituents in the cleavage process. A transposition mechanism of the molecular ion is considered to explain the two rival fragmentation schemes.     

Reaction de la bromo-3 pyridine avec le diisopropylamidure de lithium. Mecanismes de metallation et de migration d'halogene. Regioselectivite de l'addition polaire sur la pyridyne-3,4

3-bromo pyridine behaviour towards lithium diisopropyl amide (LDA) in THF is studied. A careful study of the experimental conditions point to a metallation reaction in position 4 and a “halogen dance” mechanism with isomerisation into a 4-bromo pyridine. Conversion into diisopropylamino compounds occurs simultaneously with a 3 oriented elimination-addition (EA) reaction from transient isomeric lithio-derivatives and a competing addition-elimination (AE) mechanism from the in situ formed 4-bromo pyridine.     

Etude de la Fragmentation en Spectrographie de Masse de Spiropyrannes Benzodithioliques. Influence de la Position et de la Nature des Substituants

The mass spectra of 12 benzodithiolic spiropyrans are reported. Their fragmentation pathways have been determined by exact mass and metastable transition measurements. The nature of the fragmentation is strongly dependent upon the position and nature of the substituents. A comparison is made with their photo and thermochemical decompositions.     

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.     

Heterocyclisation des α-acylaminoamides—IV : Mecanismes d'ouverture et de formation du cycle amino-5 oxazole

It was established by using ¹⁸O enriched water that the 5-aimno-oxazole cycle is opened via a nucleophilic attack of water on the 5 position. The mechanism of the heterocyclisation of ¹⁸O enriched α-acylaminoamides by trifluoracetic anhydride has been studied. Two cyclisation reactions occur, involving the attack of the anhydride by the amidic O atoms.     

Etude par Spectrométrie de Masse de la Fragmentation d'une Série de Diols Aliphatiques

The mass spectrometric fragmentation of a series of diols having the general formula HO? (CH₂)_n? OH with n = 2-11 has been studied. Extensive labelling of n-butane-1,4 diol and n-hexane-1,6 diol with deuterium allows fragmentation modes to be proposed. The labelling reveals that intramolecular exchange of H atoms often precedes the fragmentation and becomes more important when the length of the chain increases.     

Fragmentation de Triazoles Sous L'Impact Electronique—II 1,2,3-Triazole

1,2,4- and 1,2,3-triazoles behave similarly upon electron-impact; this is ascribed to the formation of common ionic structures. Metastable transitions observed for the loss of nitrogen are studied and interpreted in terms of: (i) the existance of the two tautomers of 1,2,3-triazole in the gaseous phase and (ii) the isomerisation of the molecular ion before fragmentation.     

Fragmentation de dihydro-4,7 dioxepines-1,3 par le butyllithium: Generation in situ de dienolate.

Crotonaldehyde enolate was obtained from the fragmentation of 4,7-dihydro 1,3-dioxepins by butyllithium.