Reaction Mechanisms of Gaseous Organic Cations. 20. Reactivity of Ionized 3-Phenylisoxazol-5(4H)-one

Article abstract of DOI:10.1021/jo00335a025

The chemistry of ionized 3-phenylisoxazol-5(4H)-one, which is relatively slow reacting in the gas phase, has been investigated by analysis of the mass-analyzed ion kinetic energy spectrum (MIKES), kinetic energy release, appearance energy, exact mass measurements and D, (15)N, (13)C labeling.Appropriate experiments show that the N,O-heterocyclic radical cations under study undergo unimolecular dissociations leading to the formation of benzoyl and formanilinium cations through pathways which involve phenyl migration.PhCO+ fragment ion formation must occur through a reaction channel akin to a thermochemical process.This implies a deep skeletal reorganization similar to an electrophilic substitution onto the aromatic ring and excludes the occurence of photochemical-like activation giving rise to isoxazole-oxazole ring isomerization.The decomposing ions possess, therefore, only a small excess energy, and have to follow only low-lying reaction channels.