The mass spectrometry of the ozonides of ring substituted styrenes has been studied, with R = p-CH3O,p-CH3, H,p-Cl,m-Cl, andp-NO2. Electron withdrawing substituents favor, in general, the appearance of molecular ions. The intensities of the carbonyl fragmentsfrom the fragmentation of the molecular ions follow the Hammett relationship (ρ = −0.44), as does the formation of [RC6H4CH2]+from [M-32]+(ρ = −1.36) The relative abundance of [M-32]+to that of the molecular ion is independent of R (ρ ≈ 0). The possible participation of electronically excited states in the primary fragmentation process of them-chlorostyrene ozonide has been invoked to explain its particular behaviou