Fragmentation en Spectrométrie de Masse D'Imidazobenzodiazépines

The mass spectra of a series of imidazo[4,5,1-jk]1,4-benzodiazepines and imidazo[1,5,4-ef]1,5-benzodiazepines have been examined. The differences in the fragmentation patterns permit the isomeric structures to be identified.     

Phosphates D'énols: XI—Étude en Spectrométrie de Masse des Dérivés Diméthyliques

The mass spectrometric study of a series of enolic phosphates of type A leades to fragmentation patterns influenced by the nature of the substituents (R, R′ and R″). It is generally observed that a simple or double hydrogen rearrangement occurs with the loss of the enolic groups. When R and R′ are alkyl groups, the migrating groups are the hydrogen atoms on the alkyl group at position 1. When there is no alkyl group at position 1, the hydrogen atoms of the alkyl group at position 2 induce the rearrangement process. Finally, if R, R′ and R″ are hydrogen atoms, the loss of the enolic chain occurs without any rearrangement.     

Ionisation et Fragmentation en Spectrométrie de Masse. VI—Energie d'Activation de la Fragmentation Principale des Monohalogénobenzènes

The activation energy of the fragmentation [C₆H₅X?]⁺ → [C₆H₅]⁺ + X? (X = Cl, Br, I) is calculated by various methods. These results are compared with determinations of kinetic energy release and with rate constant values available in the literature.     

Mécanismes de Fragmentation en Spectrométrie de Masse par Ionisation Chimique. IV—Fragmentation des Ions Oxiranes Protonés

Fragmentation of oxians after chemical ionization, leading to the loss of water, involves several steps. The opening of the ring is the determining step. The potential energy surface of this reaction is given for the 2-methyltetrahydrofuran.     

Spectrométrie de Masse d'Hétérocycles. VIII—Edude de Dérivés du Dioxasilolanne-1,3,2

The fragmentation mechanisms of 1,3-dioxasilolane have been investigated. These fragmentations lead principally to ‘silyl’ ion formation, or involve cleavage of the bonds α and β to the silicon as for hydrogen migrations.     

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 en Spectrométrie de Masse. IX—Fragmentation de Cyclopropanes Dicarboxylate de Méthyle-1,2 cis et trans Diversement Substitués,et des Homologues Cyclobutaniques,Cyclopentaniques et Cyclohexaniques non Substitués

A mass spectral study of cis- and trans-decarboxymethylcyclopropanes substituted on C-1, C-2, C-3 reveals that they show the same behaviour under electron impact. In every case, breaking of the carbocyclic ring is the first step giving the most important peaks. By comparing unsubstituted diesters of cyclopropane with those of the cyclobutane, cyclopentane and cyclohexane homologues, we have analysed the transmission of electronic effects by the different rings.     

Etude par Spectrométrie de Masse de Silanes et de Stannanes Aromatiques

The mass spectra of six compounds of the type Et₃Si? C₆H₄? ZR_xR_3?x (R=Et, R′ = CI, Z = Si, Sn) have been measured. The fragmentation patterns can be interpreted on the basis of an ionized hexa-1,3-diene-5-yne intermediate.     

Etude en Spectrométrie de Masse. X—Fragmentation d'Ethanes Disubstitués par un Hétéroatome des Colonnes IV,V et VI,et par un Groupement Fonctionnel

In this paper, the behaviour of ethers, sulfides, selenoethers, amines, germanes and stannanes, substituted on the β-C by a methoxycarbonyl, methyl ketone, or cyano group is compared and discussed. The compounds containing group V_B or VI_B element are quite stable, while those with a group IV_B element fragment very easily. Fragmentation α to the heteroatom gives peaks for which the intensity increases with the size of the element:[PhO]⁺<[PhS]⁺<[PhSe]⁺<[Ph₃Ge]⁺<[Ph₃Sn]⁺. Fragmentation at the β position gives very important peaks when the ionization potential is low or when the substituents inductive effect is strong (CN<CO₂CH₃<COCH₃).     

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.     

Ionisation et Fragmentation en Spectrométrie de Masse. VII—Structure de l'Ion [C6H6O]+ Issu de la Décomposition du Phényléthyléther Sous Impact Electronique

The activation energy is calculated for the fragmentation [C₆H₅OC₂H₅]⁺ → [C₆H₆O]⁺ +C₂H₄. Estimation of the enthalpy difference between the final state and the molecular ion supports the formation of a phenol-like structure for the [C₆H₆O]⁺ ion. The activation energy for backward reaction is compared with the mean kinetic energy release. Whether this is a concerted or non-concerted fragmentation is discussed.     

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.     

Spectrométrie de Masse—IV: Fragmentation des Dicétones—ϵ

The mass spectra of ten symmetrical ?-diketones are reported and a number of fragmentation patterns are documented by deuterium labelling experiments. The McLafferty rearrangement involving one of the carbonyl groups is not an important fragmentation pathway although such a double rearrangement is observed for long-chained ?-diketones. Special attention has been given to the ions resulting from the loss of either a molecule of water or the neutral species C₂H₄ which may involve an electron-impact induced formation of cyclobutanol-type ions analogous to the photochemical Yang's reaction.     

Dérivés de sucres benzimidazoliques et benzothiazoliques

Benzimidazole and benzothiazole sugar derivatives Simple aldehydosugars such as 1 or 2 , by reaction with o-phenylenediamine, gave the corresponding benzimidazoles 3 and 4 . Whereas the unperturbed α, β-unsaturated aldehydosugar D gave the benzodiazepine E upon treatment with o-phenylenediamine, the formyl-bearing alkenyl acetals 5 and 8 led, in the same conditions, to the benzimidazoles 6 and 9 respectively or, on reaction with o-aminothiophenol, to the benzothiazoles 7 and 10 respectively. This difference in reactivity is explained by the electrondonor ability of the oxygen atom of the alkenyl acetal function as shown by the ¹³C-RMN. spectra.     

Orientation de la Fragmentation en Spectrométrie de Masse Par Introduction de Groupements Fonctionnels. XII—Ethylene Acetals Derives de Cyclopentanones et Cyclopentanones α Substituees

The mass spectrometric fragmentations of ethylene ketals corresponding to α substituted ketones were re-examined. A new type of rearrangement has been established.     

Étude en RMN du 13C de Dérivés de la Pipéridone-4 Stériquement Encombrés et des Oximes Correspondantes

The regiospecific differences in chemical shifts caused by the oximino group, such as Δδ as Δδ parameters, are useful to estimate conformational distortions directly from ¹³C spectra. Particularly, twist-boat conformations resulting from oximation of sterically hindered piperidones are unambiguously detected.     

Spectrométrie de Masse d'Hétérocycles Azotés. VII—Phenyl-1 Triazole-1,2,3

Comparison of the ‘normal’ and mass analysed ion kinetic energy spectra of 1-phenyl-1,2,3-triazole and a few D and ¹³C labelled derivatives indicates that the ions may follow two competing decomposition pathways: a simple rupture without rearrangement is preferred by the ions of high internal energy content (normal spectrum). On the other hand, for low internal energy metastable ions, loss of HCN is more important and occurs after a complete randomization of the H atoms.     

Spectrométrie de Masse d'Hétérocycles Azotés. X–Contribution à l'Etude du Comportement de ll'Ion Aniline et des Ions Aminopyridines avant Fragmentation par Perte de HCN

The study of the mass analysed ion kinetic energy spectra of deuterated derivatives of aniline, aminopyridines and 2-chloro-5-aminopyridine shows that prior to HCN loss, hydrogen scrambling does not occur for aminopyridines and is limited but noticeable for aniline. In the case of this last compound the extent of scrambling varies markedly for small variations in the energy of the ions studied, these variations being within the energy window corresponding to metastable ions. Furthermore, an examination of the mass analysed ion kinetic energy spectra of monodeuterated derivatives of aminopyridines leads to the rejection of the generally accepted mechanism for HCN loss from the molecular ions of these compounds.     

Spectrométrie de Masse D'Hétérocycles Azotés. VI—Tautomérie en Phase Gazeuse d'Isoxazolones-5

A comparison of the fragmentation under electron impact of isoxazol-5-ones with those of their methylated derivatives (5-methoxy isoxazoles, 2-methyl isoxazol-5 ones and 4-4-dimethyl isoxazol-5 ones) shows that in the vapor phase and prior to the fragmentation, the isoxazol-5 ones exist in the CH tautomeric form. Furthermore, in the case of the 5-methoxy isoxazoles, it has been established that the rearrangement isoxazole→azirine→oxazole which occurs thermally, leads to a variation in the intensities of some ions depending on the experimental conditions.