MASS-SPECTRA OF ALKYL-4-PHENYL-4-IMIDAZOLIN-2-ONES AND PHENYL-4-IMIDAZOLIN-2-ONES

The mass spectra of a variety of alkyl‐ and aryl‐4‐imidazolin‐2‐ones have been determined and the fragmentation mechanisms have been analyzed by deuterium labelling, high resolution and metastable transitions allowing certain differentiations of positional isomers. In contrast to the benzoid systems the mass spectra of isomeric alkyl‐4‐imidazolin‐2‐ones are distinctive. The influence of the position of substituents is demonstrated by phenyl‐4‐imidazolin‐2‐ones establishing an exact prediction of fragmentation pathways. Fragment ions (e.g. [M‐HNCO].+) which are the result of rearrangement processes were excluded for structure determinations. The ion structures involved were elucidated by collisional activation comparing model ions. Alkyl‐phenyl‐4‐imidazolin‐2‐ones give almost identical mass spectra, but the positional isomers can easily be distinguished by different fragmentation patterns in both metastable and collisional activation spectra of the molecular ions. Copyright © 1979 Journal of Heterocyclic Chemistry