Electron impact mass spectra of 6-substituted 12H-tetrachlorodibenzo

Bis(2-hydroxy-3,5-dichlorophenyl)methane and its cyclized derivatives (6-substituted 12H-tetrachlorodibenzo[d,g] [1,3, 2]dioxaphosphorin-6-oxide and sulfides) were analyzed by EI-MS, and the mass spectra are discussed. It was shown that the mass spectra of the cyclized derivatives are rather different from that of the parent compound. The relative roles of the S and O atoms were very important, and led to special ions which could indicate certain moieties within the molecular structure. Thus, the fragment ions at m/z 63 and 333 indicate a cyclic structure with a (P=S) group, while m/z 397 indicates P(=S)S or P(=S)-Cl) moieties, and m/z 380 with high intensity indicates P(=O)O. Copyright 2000 John Wiley & Sons, Ltd.     

The mass spectra of 3-substituted furans

A fragmentation pattern characteristic of 3-substituted furans, in which the 3-substituent carries an oxygen function, is discussed. Examination of the spectra of some meliacins, as well as those of some synthetic model compounds, illustrates the diagnostic value of this particular fragmentation. In addition the spectrum of methyl limonilate (III, R = CH₃) is discussed in some detail.     

Field ionization and electron impact mass spectra of cycloolefins

The field ionization mass spectra of monosubstituted cyclopentenes and cyclohexenes with C₁-C₇ n-alkyl and C₄-C₅ isoalkyl substituents in positions 1 and 3 have been investigated and compared with the previously reported electron impact mass spectra of these compounds. The cleavage of the C? C bond β to the double bond in the non-isomerized molecular ion was found to be a typical degradation reaction of the higher homologues in the strong electric field. So, by means of the field ionization mass spectra, the >C₁ alkyl substituent can be readily located in the parent molecule. The electron impact mass spectra exhibit a less specific fragment ion distribution for positional isomers due to the extensive molecular ion isomerization prior to decomposition, but provide useful information on the ring size. For structure determination it is appropriate to use both ionization techniques.     

Mechanism of ionization and initial fragmentation in electron impact mass spectra of 3-halogenobenzanthrones

Electron-impact mass spectra of 3-halogenobenzanthrones (halogen X = Cl, Br, I) were measured and ionization efficiency curves and three kinds of linked-scan spectra were obtained for several fragment ions. The fundamental mechanisms of ionization and initial fragmentation were interpreted by the penetration length of an impacting electron or the density distribution on the molecular surface of a rejected electron and its orbital energy. The apparent ionization energy (IE) of a singly charged molecular ion seems to be the lower one of non-bonding electrons on O or X, and that of a doubly charged molecular ion the sum of three terms, the IE of non-bonding electron on O, that on X and the electrostatic repulsion between two positive charges. Two competing pathways of decomposition from the molecular ion M^+· to an ion [M - CO,- X]⁺ were observed: one is the initial detachment of CO in chloro and bromo compounds and the other is the initial elimination of the iodine atom in the iodo compound. The sequence of these reactions was confirmed by metastable ion analysis with linked-scan spectra and the relative magnitudes of the appearance energies. They can be explained by the driving force of a localized positive charge or unpaired electron on a heteroatom.     

The electron impact and chemical ionization mass spectra of dimethyltrisulfide

Summary The mass spectra obtained by electron impact ionization (EI) of dimethyltrisulfide, both at constant sample pressure and during elution from a GC column, are essentially identical, with the molecular ion Me₂S ₃ ⁺ providing the basis peak. Masses heavier than the molecular ion are not observed. Chemical ionization, using nitrogen, methane or isobutane, gives rise to numerous ions of larger mass than that of the molecular ion. Particularly characteristic are sulfonium type structures Me₃S _n ⁺ , with n=3–6. In addition, radical cations of the type Me₃S_nCH ₂ ⁺ and protonated trisulfide, Me₂S₃H⁺, are observed, even with N₂ as ionizing gas, together with a variety of ions of lower hydrogen content. Further, a large number of ion types of lower mass than the parent molecule are formed. The mass distribution of ions in the spectrum is found to be highly dependent on the partial pressure of dimethyltrisulfide in the ion source. These phenomena were investigated and accounted for semiquantitatively.

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Die EIund CI-Massenspektren des Dimethyltrisulfids

Zusammenfassung Dimethyltrisulfid liefert nach Elektronenstoßionisation bei konstantem Probendruck und bei GC-Probeneinlaß im wesentlichen identische Massenspektren. Das Molekülion Me₂S ₃ ⁺ stellt dabei den Basispeak dar. Größere Massen als die des Molekülions wurden nicht beobachtet. Bei chemischer Ionisation unter Verwendung von Stickstoff, Methan oder Isobutan als Reaktantgas entstehen zahlreiche Ionen mit höherer Masse als der des Molekülions. Charakteristisch sind hierbei sulfoniumartige Strukturen Me₃S _n ⁺ mit n=3–6. Daneben beobachtet man Radikalkationen des Typs Me₂S_nCH ₂ ⁺ und protoniertes Trisulfid Me₂S₃H⁺ auch bei Ionisation mittels N₂ sowie Ionenarten mit einem geringeren Wasserstoffgehalt. Weiterhin wird eine größere Anzahl von Ionenarten gebildet, deren Massen kleiner sind als die des Stammoleküls. Die Massenverteilung der Ionen im Spektrum hängt außerordentlich stark vom Partialdruck des Dimethyltrisulfids in der CI-Quelle ab. Diese Abhängigkeiten wurden semiquantitativ untersucht und dargestellt.

     

The electron impact mass spectra of some rotenoid derivatives

The fragmentation behaviour of several rotenoids functionalized in the alicyclic portions of the molecule is described.     

The electron impact mass spectra of some cevine orthoacetates

The most important fragmentation in the electron impact mass spectra of dihydrocevine orthoacetate and some analogues involves loss of an acetoxyl radical from the molecular ion, and is associated with strain in the orthoacetate group bridging a six-membered ring. The process is much less important in the less-strained dihydrocevine isoorthoacetate, which gives the ion m/z 112, characteristic of cevine alkaloids, as the most abundant. A further important difference concerns an ion involving the loss of C(20) and its substituents together with a hydrogen atom from M⁺˙, also relatively unimportant in the isoorthoacetate.     

Chemical ionization and electron impact mass spectra of alicyclic substituted 2-aryl-1,3-dithianes

The methane and isobutane chemical ionization mass spectra of alicyclic substituted 2-aryl-1,3-dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.     

The fragmentation of 5- and 3-substituted thiophene-2-carboxamides under electron impact

The 70 eV electron impact mass spectra of twelve 5- and 3-substituted thiophene-2-carboxamides are discussed with the aid of exact mass measurements and labelling experiments. All mass spectra exhibit pronounced molecular ions. Some isomeric 5- and 3-substituted title compounds can be differentiated by mass spectrometry. The fragmentation is influenced by a strong ‘ortho-effect’ which activates the NH₃ elimination. In the other cases the most important fragmentation is NH₂˙ loss, followed by CO elimination.     

Stereochemical effects in the electron impact mass spectra of some 2,6-dideoxy-3-c-methylhexopyranoses

The electron impact mass spectra of the methyl α-and β-glycosides of axenose, of a number of derivatives, and of mycarose, display substantial differences, characteristic of their stereochemistry. In order to interpret this behaviour the structures of the fragments and the main features of the fragmentation patterns have been established, and the methyl glycosides of some related monosaccharides (arcanose, cladinose and idose) have been examined. The experimental results allow the observed differences to be attributed to the presence of an intramolecular hydrogen bond between the hydroxyl group at C-3 and the oxygen atom of the methoxy group in the methyl α-glycosides of axenose and mycarose.     

Differentiation of isomeric cyclic diamides by electron impact mass spectra

The behaviour under electron impact of two series of isomeric cyclopentane- and cyclohexane-1, 2- and -1, 3-dicarboxylic acid dipiperidides was studied. Diagnostic fragmentation pathways were found to differentiate the isomeric diamides. Additional evidence was obtained from the metastable transitions.