Mass spectrometric behaviour of simple oxazolidines under electron impact and chemical ionization

The 70 eV electron impact mass spectra of 33 differently substituted oxazolidines were studied to determine the effect of substituents and the existence of the ring—chain tautomeric equilibrium on the decomposition of the molecular ions. Most of the fragmentations can be rationalized to start as the cleavage initiated by the radical site at nitrogen. Isomeric compounds showed different spectra and were easily differentiated. The position of the ring—chain equilibrium could be located only roughly. The chemical ionization mass spectra of the compounds were also recorded, with ammonia, isobutane, acetone or methane as reagent gas. Methane was the only reagent gas that promoted extensive fragmentation of the protonated molecules. However, no information about the position of ring-chain tautomerism was obtained under these conditions. Analogously to other related five-membered heterocycles, the oxazolidines reacted under acetone chemical ionization conditions to afford [M + CH₃CO]⁺ adduct ions. These adducts were stable, however, and unlike those of 1,3-dioxolanes and 1,3-oxathiolanes, they did not decompose and form stable oxonium ions.