Abstract: | The mass spectra of six-membered saturated heterocycles containing oxygen, sulphur, selenium and tellurium in the 1,4-positions have been measured. The differing fragmentation modes have been characterized using high resolution, low voltage and metastable ion scan techniques. The important decomposition reactions of the molecular ions involve elimination of C2H4 and CH2X (X is a chalcogen atom) and formation of [C2H4X]+ and C2H5+. The propensities of these reactions vary systematically as a function of the ability of the chalcogen to stabilize a positive charge. |