N,N'-Diisopropyl-substituted 1,3,4-oxadiazolidine 3e, 1,3,4-t,hiadiazolidine 6, 4,5-benzo-1.2,3,6-tetrahydropyridazine 8, and new 3,4-dialkyl-l,3,4-oxadiazolidines 9--14 were synthesized and studied. The configurationa{ stability of the N atoms does not change on going from compound 3r to its S-analog 6 and decreases in the case of pyridazine 8. 3,4-Di-tertalkyl-l,3,4-oxadiazolidines 3d and 11--14 were found to be promising objects for optical resolution.

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The behaviour of compounds I to XI1 under electron-impact (electron voltages 30 and 12 eV) was investigated. The abundance of the ions characteristic of amines was shown to decrease drastically with an increase of chain branching in alkylphosphines. Comparison of the spectra of VII and X led to the conclusion that the unshared electron pair of phosphorus does not affect the fragmentation. The main peaks in the spectra of phosphines corresponded to hydrocarbon fragments. The origins of the main fragment ions were confirmed by metastable peaks.

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