The mass spectra of phenothiaphosphine derivatives

The molecular ion of the phenothiaphosphine derivatives is fairly stable. Under electronimpact, the phenothiaphosphines (I) and phenothiaphosphinic acids (IV, R = H) undergo a one-step elimination of the phosphorus atom together with the groups attached to it. Substitutents in the aromatic rings, as well as on the phosphorus, influence the fragmentation pattern; ring methyl, e.g. leads to tropylium structures. Phosphine oxides of type V lose RO˙, probably after a rearrangement, when R = aryl, but R˙ if it is methyl.     

The mass spectra of some pentafluorophenylthio derivatives

Ionic fragmentations induced by electron-impact on compounds of the type C₆F₅SX (X ? H, CH₃, COCH₃, Cl, C₆F₅) and (C₆F₅S)₂, (C₆F₅S)₂Hg, (C₆F₅S)₃As and (C₆F₅SCH₂)₂ have been studied. Principal features of the mass spectra are reported. The [C₆F₅S]⁺ ion (m/e 199) is predominant and its mode of fragmentation has been deduced. The precursor ions for m/e 199 have been examined in (C₆F₅)₂S, (C₆F₅S)₂, (C₆F₅S)₂Hg, (C₆F₅S)₃As and C₆F₅SCl. Ion kinetic energy spectra of (C₆F₅)₂S, (C₆F₅S)₂, (C₆F₅S)₂Hg and C₆F₅SCl have been recorded, and all contain peaks corresponding to the fragmentation of the [C₆F₅S]⁺ ion.     

The mass spectra of eleven derivatives of cyanocyclopropane

Studies of the mass spectrum of 1,2-diphenyl 1-cyclopropane show that a large number of fragmentations and rearrangements take place during the electron-impact of this compound. The mechanisms involved were identical to those found in the studies previously made on the cyclopropanes. Other patterns of fragmentations and rearrangements will also be shown, resulting from the presence of the cyano and substituted diphenyl groups linked on the propanic ring. The nature of the para substituent is fundamental to the aspect of the mass spectra.     

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 mass spectra of some C-19 modified cholesteryl derivatives

The mass spectra of twenty one C-19 modified cholesteryl derivatives have been determined and compared with results for related systems. In the case when the hydrogen(s) of the C-19 group have been replaced by other groups the metastable evidence shows that in those molecules with a C-3 hydroxyl group the loss of water followed by the loss of the C-19 group gives rise to an intense ion at m/e 353, whereas the loss of the C-19 group with hydrogen transfer to the ion, followed by the loss of water gives rise to the large ion at m/e 354. In contrast in the case of the C-3 acetates the main fragmentation is the loss of acetic acid followed by the loss of the C-19 group to give the ion at m/e 353. This is rationalised on the basis of results observed in other systems. In the case of the C-3 tosylates evidence for pyrolysis before electron impact fragmentation is presented. The subsequent fragmentation of the large ions at m/e 354, 353 and other m/e values in the high mass region is shown to be in line with earlier work.     

Fluorinated carbohydrates—IX The mass spectra of deoxyfluorohexopyranose derivatives

The mass spectra of some deoxyfluorohexopyranose acetates bearing the fluorine substituent at positions 2,3,4, or 6 were determind. The fragmentation pathways were analogous with those for hexopyranose acetates, except that the cleavage of bonds between carbon atoms was hindered by the attachment of a fluorine substituent to one of the carbon atoms.     

The mass spectra of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives

The mass spectra of a series of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives have been determined. Fragmentation mechanisms are supported by high resolution, deuterium labeling and metastables.     

Synthesis of new quinoxaline derivatives

Proceeding from 2-aminoquinoxaline-3-carbonitrile 1,4-dioxides new derivatives of quinoxaline and quinoxaline 1,4-dioxide were synthesized containing in the position 3 of the quinoxaline fragment 1,2,4-oxadiazole and tetrazole rings. The acylation of 2-amino-N′-hydroxyquinoxaline-3-carbox imidoamide 1,4-dioxide was investigated.     

The mass spectra of 1,2,4-triazine and some of its derivatives

The mass spectra of some esters of 1,2,4-triazine-3-carboxylic acid and of 1,2,4-triazine itself are reported, and their fragmentation patterns are analyzed. The syntheses of the methyl and of the t-butyl esters of 1,2,4-triazine-3-carboxylate are described.     

Palladium-catalyzed synthesis of quinoxaline derivatives

A palladium-catalyzed reductive N-heteroannulation of enamines derived from 2-nitrobenzenamines forming mixtures of 1,2-dihydroquinoxalines and 3,4-dihydroquinoxalin-2-ones is described. The reactions are performed using bis(dibenzylideneacetone)palladium(0), 1,3-bis(diphenylphosphino)propane, and 1,10-phenanthroline in DMF under 6 atm of carbon monoxide at 70 °C.     

o-nitroaniline derivatives. IV—The mass spectra of o-nitroanils

The principal feature of the mass spectra of o-nitroanils, ArCH?NC₆H₄NO₂(o-), is an intense peak corresponding to the [ArCO]⁺ ion; this implies oxygen transfer from the nitro group to the azomethine carbon during the fragmentation process. In this series of anils, loss of OH from the molecular ion is not apparently an important fragmentation pathway, in contrast to the fragmentation of o-nitrobenzylideneanilines. Benzylideneaniline derivatives with an o-nitro substituent in both rings have mass spectra which indicate interaction of both nitro groups with the ? CH?N? group, but in this series of spectra the [M—17]⁺ ion is again of low intensity.     

The mass spectra of some N-substituted barbitals and their trimethylsilyl derivatives

The mass spectra of N-propyl and N-butyl barbitals show the loss of olefin radical (C_nH_2n-1) in analogy to structurally similar molecules such as N-alkyl succinimides and 3-alkyl uracils. Trimethylsilylation of the N-substituted barbitals suppresses this fragmentation and loss of olefin via apparent McLafferty rearrangement from the even-electron ion, [M – 15]⁺, becomes significant. The trimethylsilyl derivatives of N-allyl barbital and N-phenyl barbital show an unusually facile elimination of the appropriate isocyanate from the molecular ion.     

Electronic spectra of quinoxaline 1-N-oxides

The nature of theπ→π ^* transitions in the spectra of quinoxaline 1-N-oxides as compared with unoxidized quinoxalines was examined on the basis of an experimental, study and calculation by the Pariser-Parr-Pople configurational interaction method.     

Pyrolysis and mass spectra of trimethylsilyl derivatives of monosaccharides

The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose相似文献