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The mass spectra of 20 1,Idithianes were studied. The fragmentation patterns including the loss of 74 u and 107 u and clearage of the substituent at C-2 depended strongly on the nature of the substituents at that position. 2,2-Diphenyl-1,3-dithiane undergoes an atypical fragmentation with the formation of a fluorene skeleton.

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Under El conditions, substituents on N‐alkylpyrroles affect fragmentation of the alkyl groups. The electron‐withdrawing character of the cyano group retarded formation of a N‐methylene cation, and a labile substituent, i.e., ‐CHO, ‐CH2COOMe, competed with an N‐alkyl group to be a initial fragmentation center, MNDO calculation of the heat of formation of possible fragment ions showed that protonated pyridine is the most stable among the isobaric ions.