Electron impact mass spectra of polycyclic aromatic compounds with several types of pyridino‐ and benzobenzanthrone skeletons

Abstract

Electron impact mass spectra were measured for five isomers of pyridinobenzanthrones and three isomers of benzobenzanthrones. The fragmentation pattern and intensity of M", [M -HI', [ M -CO]'+, [M -CO -H(or 2H)I" and [ M -CO -HCN]" (i = 1, 2) ions indicated remarkable differences and very interesting features according to the isomers with or without nitrogen and condensation positions of a pyridino or benzo ring to the benzanthrone skeleton. Further, the competition of decompositions through [ M -HI', [M -CO]" or [M -HCN] + * ions was confirmed by the observation of metastable ions and the appearance energies of fragment ions. Interesting observations from these results were expulsion of an H atom in close proximity to the area around an O=C group, a weak bonding interaction between sp2 C-H and an O=C group, inducing specific hydrogen rearrangement, and characteristic charge localization on heteroatoms.

The effect of protonation site on bond strengths in simple peptides: Application of Ab initio and modified neglect of differential overlap bond orders and modified neglect of differential overlap energy partitioning

“…As mentioned above, the corresponding MNDO bond orders are very small: 0.002 and 0.006, respectively ( Figure 2). (Note that our MNDO energy partitioning contributions for H bonds are in good agreement with MNDO-PM3 values reported recently by Abliz et al [42] for pyridinobenzanthrones and benzobenzanthranes. )…”

Characteristic elimination reactions of 1,2‐disubstituted phenylbenzimidazoles and their isosteres 2,3‐disubstituted phenylindoles in electron ionization mass spectrometry

“…The nitrogen atom in the 1‐position of type I compounds appears to be necessary for formation of the [MH] + ions. The crab‐like position8–11 of the phenyl rings (i.e., C‐2′ and C‐2″) is also involved in the cyclization; this interpretation is supported by the spectra of 15 – 20 (type I b ) in which the ortho substituents interfere sterically with the cyclization reaction and thus lead to a lower probability of hydrogen expulsion, as observed by a significant reduction in the relative intensity of the [MH] + peak. Thus the chief driving force for cyclization appears to be the availability of the aromatic ring nitrogen N‐1 for inducing a radical‐like reactive site on C‐2′ or C‐2″, and the resonance stabilization of both the radical and charge sites in the resulting cyclic ion.…”

Unexpected formation of [M]2+ from [M+CuCl+H]2+ ions under CID conditions, where M is a molecule of 3,5-bis(2,2’-bipyridin-4-ylethynyl)benzoic acid or its methyl ester

“…These ions, also called molecular ions, are formed by the loss of one electron from the neutral organic molecule. Observations of the loss of two electrons leading to doubly charged ions [M] 2+ (di-cations) under EI conditions have been very rare [1][2][3][4][5][6]. Under electrospray ionization (ESI) conditions, organic radical cations [M] +• also can be formed, and this phenomenon is quite well known.…”