Mass spectral study of isomeric benzoxazolinones by electron ionisation

Abstract

The electron impact mass spectra of isomeric dihydrofurobenzoxazolinones, (1–3), hydroxy (2-methyl-2-propenyl)benzoxazolinones (4–5) and (2-methyl-2- propenyloxy)benzoxazolinones (6–7) are studied. The mass spectra of 1–3 show differences in the relative abundance of an ion at m/z 163. A mechanism involving the heteroatom of the benzoxazolinone ring which is para to the oxygen of the dihydrofuran ring has been proposed to explain the results. The mass spectra and collision-induced dissociation spectra of molecular ions of 4 and 5 are similar to those of 1 and 2, respectively, suggesting the rearrangement of 4 and 5 to 1 and 2, respectively, in the source of the mass spectrometer. The fragmentation of 6 and 7 supports the proposition of dihydrofuran ring opening in 1–3. The fragmentation of 6 and 7 is different in comparison to 4 and 5, suggesting that 6 and 7 do not rearrange to 4and 5, respectively, either before or after ionisation.