Mass spectrometric fragmentation

The mass-spectrometric fragmentation of 2-aminothiazole-3-oxides is characterized by the abstraction of O and OH out of the molecule ion. Variations observed in the mass spectra suggest an equilibrium between tautomers 354a and 354b in the gas phase (Scheme 203). 

QET. quasi-equilibrium theory (of mass spectrometric fragmentation)... 

The electron impact mass spectrometric fragmentations of (E)-3- and ( )-4-styryl-pyridazines show that the intensity ratio of the M and (M -1)" ions, the general degree of fragmentation and the elimination pathways of nitrogen are the most characteristic features distinguishing between the two isomeric compounds (81JHC255). 

A mass spectrometric study was carried out to establish tbe structure of compoimd 69. Its mass spectrum contains tbe molecular ion peak m/z 252 (16.98%) and a base peak (100%) at m/z 210, corresponding to 2-(2-hydroxypbenyl)benzimidazole (70). A tendency towards decreasing the heterocycle size is characteristic of the mass spectrometric behavior of 1,5-benzodiazepin-2-ones [61] and consequently the mass spectra of these compounds contains intense peaks of the corresponding benzimidazoles. It is also known that the mass spectrometric fragmentation of 1,5-benzodiazepines is similar to their thermal or acid decomposition. In fact, refluxing compound 69 in concentrated sulfuric acid yields benzimidazole 70 as the main product. 

Formation of the metaphosphonate 23 also occurs on mass-spectrometric fragmentation of the 1,3,4X5-dioxaphosphorin 56a 17 35> a peak at m/e = 140 corresponding to the mass number of 23 is indeed observed 35). Vacuum pyrolysis of 56a parallels the mass spectrometric degradation to form diphenylacetylene and benzophenone however, 23 could not be detected directly. This can be accomplished though, if thermolysis is conducted in methanol (220 °C/22 at) dimethyl benzenephosphonate (63) is again formed via 62 35). 

Lavanchy, A. Houriet, R. Gaumann, T. The Mass Spectrometric Fragmentation of ra-Heptane. Org. Mass Spectrom. 1978, 75, 410-416. 

Hrasak, J. MNDO Calculations on the Neutral and Cationic [CH3-CO-R] Systems in Relation to Mass Spectrometric Fragmentations. Z Phys. Chem. 1991, 772, 217-226. 

Griitzmacher, H.-F. Mechanisms of Mass Spectrometric Fragmentation Reactions. XXXII. The Loss of Ortho Halo Substituents From Substituted Thiobenzamide Ions. Org. Mass Spectrom. 1981, 16, 448-450. 

Nakano, T. Martin, A. Mass Spectrometric Fragmentation of the Oxetanes of 3,5-... 

In another paper, the main El fragmentation processes of three pairs of diexo- and diendo-iased l,4,4a,5,8,8a-decahydro-5,8-methano-2//-3,l-benzoxazin-4-ones 374 (91IJM225 91MI2) were established by means of mass spectrometry and MNDO calculations. The El mass spectrometric fragmentations of the bis-oxazinones 375 have also been reported [79ACH(101)61]. 

Current detection limits are < 1 ng for full scan mass spectra and < 1 pg for multiple ion monitoring mass spectrometry. Compound identifications are based on the comparisons with authentic standards, GC retention time, literature mass spectra and the interpretation of mass spectrometric fragmentation patterns. The MS methods used for the various markers and studies are listed in Table 1. 

Mass spectrometric fragmentation of substituents and rings are presented in Table 14. Among further examples, enamine 184a shows (M — nitrophenyl) as the base peak, a behavior typical of 1,4-dihydropyr-idines (77LA1888). Tetrabrominated lactam 347 (see Scheme 78) gives a... 

Figure 12 Principal mass spectrometric fragmentations for pyrrole...

Figure 21 Proposed mass spectrometric fragmentations for methylindolizines...

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