AbstractUnder El conditions, substituents onN‐alkylpyrroles affect fragmentation of the alkyl groups. The electron‐withdrawing character of the cyano group retarded formation of aN‐methylene cation, and a labile substituent, i.e., ‐CHO, ‐CH2COOMe, competed with anN‐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 is