Electron Ionization Mass Spectra of Some Diexo Norbornane- and Norbornene-fused Phenyl-substituted 1,3-Oxazines and Related Systems. Competitive retro-Diels-Alder Fragmentations in 4-Phenyl-4a,5,8,8a-tetrahydro-5,8-methano-4H-benzo[e]1,3-oxazines

The mass spectral behavior of 2,3-dihydro-4H-1,3-oxazin-4-ones has been investigated using electrospray ionization multi-stage mass spectrometry (ESI-MS(n)). All compounds showed a predominant retro-Diels-Alder (RDA) fragmentation pathway, and a novel ring contraction reaction by loss of isocynates was also found. The fragmentation mechanisms proposed for 4H-1,3-oxazin-4-ones are supported by ESI-MS/MS/MS spectra.

Ring contraction reactions of 2,3‐dihydro‐4H‐1,3‐oxazin‐4‐ones under electrospray ionization conditions

Liu

Chen

et al. 2004

Electron ionisation induced fragmentation of fused norbornene analogues containing SiMe₂ or GeMe₂ and oxygen bridges. Migration of SiMe₂ and GeMe₂ groups

Eckert‐Maksić

Kazazić

et al. 2001

The main electron ionisation induced fragmentation processes of fused norbornene analogues containing SiMe2 or GeMe2 and oxygen bridges, as well as their dependence on substitution, were investigated using mass (MS) and tandem mass (MS/MS) spectrometric analysis. Formation of the rearrangement ions of m/z 176 in the mass spectra of fused norbornene analogues containing SiMe2 and m/z 222 in the mass spectrum of norbornene analogues containing GeMe2 provides firm evidence for the migration of a SiMe2 and GeMe2 bridge, respectively.

Differentiation of diastereomeric N‐aryltetrahydropyrano/tetrahydrofuranochromenylamines under electron ionization and chemical ionization conditions

Ramanjaneyulu

Prabhakar

Bhaskar

et al. 2007

A series of diastereomeric 4S,5S,6R/S-tetrahydropyrano- and 3S,4S,5R/S-tetrahydrofuranochromenylamine derivatives (a/b isomers; 1-26) has been studied under electron ionization (EI) and chemical ionization (CI) conditions. The EI mass spectra of all diastereomeric compounds show two characteristic fragment ions, of which one is formed by retro-Diels-Alder (RDA) reaction from the molecular ion, retaining the charge on the diene fragment, and the other [M-(HNAr)]+ ion by a simple radical loss. The RDA process is more favorable in all b isomers, whereas the radical loss is dominant in all a isomers; based on these two ions it is easy to differentiate the two diastereomers. The collision-induced dissociation (CID) spectra of all the molecular ions also show the same trend, which reflects the stereoselectivity in the formation of the two characteristic fragment ions. The results of theoretical calculations performed are in accordance with the experimental observations. The CI experiments (methane and isobutane) on all the diastereomeric compounds also enabled the differentiation of the isomers.