The relative rates for the gas-phase dissociation RX+→ R++ X° of five (4-Y-substituted benzyl) dimethysulfoniums (Y= MeO, Me, H, Cl, and NO2) and 24 (4-Y-substituted benzyl)-3'- Z-pyridiniums (complete series for Z= CN, Cl, CONH2, and H, and 4-methoxy-and 4- nitrobenzyls for Z= F and CH3CO) were measured using liquid secondary ion mass spectrometry. The Hammett plot (vs δΔ G° or σ+) is linear for the sulfoniums, but plots for ...