Electron-impact and thermal fragmentation patterns of some perfluoroalkylene-linked aromatic and heteroaromatic compounds

The pyrolysis of some perfluoroalkylene-linked aromatic and heteroaromatic polymer precursors and a poly(1,3-phenylenehexafluorotrimethylene) has been studied using a combined pyrolysis-gas chromatographic-mass spectrometric method. Whereas the electron-impact induced fragmentations of the polymer precursors are almost exclusively controlled by cleavage β to the aromatic or heteroaromatic ring, thermolysis of these compounds yields products whose formation is consistent with the occurrence of primary cleavage processes that are not confined β to the ring.     

The reaction of epibromohydrin with hydroxyquinazolin-2-(1H)one derivatives. Novel oxazine formation

Epibromohydrin was found to react with 7-hydroxy-2-methylpyrrolo[1,2-c]quinazolin-5(6H)-one ( 4 ) in the presence of sodium hydroxide to form the novel oxazine 5 . The structure of compound 5 was proven by cmr and pmr analysis.     

Pyrolysis and mass spectra of some aromatic-imides

The electron-impact induced loss of CO₂ from phthalanil and 4-phthalimidobiphenyl is paralleled by the formation of large amounts of CO₂ on pyrolysis. CO is also a major pyrolysis product, but the loss of CO from these compounds under electron-impact is not an important fragmentation process. The mass spectra of meta and para-chlorophthalanils show prominent [M ? CO₂] peaks but the corresponding peak for the ortho isomer is of relatively low intensity. CO and CO₂ are the principal gaseous products of the thermal decomposition of o-chlorophthalanil.     

Mass spectra of some azoles

The principal electron-impact fragmentation patterns of 3,4,5-triphenyl-1,2,4-triazole, 2,5-diphenyl-1,3,4-thiadiazole, their perfluorinated analogues and 2,5-di(pentafluorophenyl)-1,3,4-oxadiazole have been established from metastable ion evidence and precise mass measurements. Although ions produced by expulsion of nitrogen from the molecular-ions of these compounds are of low abundance, the simultaneous expulsion of nitrogen and a C₇X₅ radical (X = H or F) gives rise to abundant ions.     

Endothermic ion molecule reactions

Endothermic ion-molecule reactions in a tandem mass spectrometer have been used for a number of years for determining thermodynamic quantities, such as heats of formation and proton affinities, for gaseous ions. Recently, the reactive, endothermic collision has been exploited as an analytical technique for the structural analysis of peptides and other biomolecules. The technique is based upon the endothermic transfer of protons associated with amide bonds to ammonia. This reaction proceeds via a long-lived collision complex. When additional beam energy is supplied, other dissociation channels are opened up, leading to the production of sequence ions for the mass-selected, protonated analyte that are normally observed in high energy collision-induced dissociation spectra. The advantage, however, is that such spectra can be produced at very low beam energies. In this article, the rationale for developing this scheme, and its roots in previous ion-molecule studies, are explored.