Mass Spectral Study of Some Stereoisomeric 2-Thioxo- and 2-Oxo-perhydro-1,3- and 2-Thioxoperhydro-3,1-benzoxazines.

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Abstract
Mass spectral fragmentations of tetrahydro-1,3-oxazine-2-thione, six 2-thioxo- and three 2-oxo-perhydro-1,3- or -3,1-benzoxazines have been examined using metastable ion analysis and exact mass measurement. The fragmentation patterns of the 1,3-benzoxazines clearly differs from those of the 3,1-benzoxazines making it easy to distinguish them from each other. However, the cis- and trans-fused isomers gave rise to quite similar spectra, although comparison of some fragmentations which favoured one or the other isomer made structural identification possible. The trans-fused isomers were always more resistant to fragmentation than the corresponding cis forms. In contrast with the thioxo compounds, oxo compounds were very unstable under electron ionization. No gas-phase enolization or thienolization could be found with the compounds studied.

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