AbstractThe main process of the electron impact induced water elimination of the title compounds takes a reaction course comprising several individual steps. A characteristic neighbouring group participation of the carbonyl function is involved, onto which a hydrogen is transferred in a first rate‐determining reaction step. This rearranged hydrogen is finally lost together with the hydroxyl group. The reaction ofN‐(2′‐hydroxyethyl)piperidone follows what seems to be a [1,1] elimination whereas the H2O elimination fromN‐(3′‐hydroxypropyl)piperidone represents a formal [1,2