Energy and substituent effects on gaseous ionic decompositions: Electron and charge exchange ionization of benzophenones and benzils

The correlation with substituent constants reported previously for [YØCO]⁺/[ØCO]⁺ ratios in the electron ionization mass spectra of substituted benzophenones and acetophenones has also been observed in the electron ionization spectra of substituted benzils. The [YØCO]⁺/[ØCO]⁺ ratio for the substituted benzils varied with energy of the ionizing electrons according to predictions from a simple kinetic and thermochemical analysis. [YØCO]⁺/[ØCO]⁺ ratios in the charge exchange spectra of benzophenones obtained with Xe, Kr, CO, N₂ and Ar gave good correlations with sub-stituent constants in agreement with the same analysis. Good correlations were also noted for [YØCO]⁺/[ØCO]⁺ ratios with substituent constants for [M]⁺ ions of the benzophenones of the same excess energy (5.5 eV). [YØCO]⁺/[ØCO]⁺ ratios for benzils obtained by charge exchange with [CO]⁺ also showed good correlations with substituent constant. It is suggested that [Ø]⁺ and [YØ]⁺ ions from the benzophenones may be formed primarily by one step decompositions of the molecular ions, but that the [Ø]⁺ and [YØ]⁺ ions from the benzils are formed primarily by decomposition of [ØCO]⁺ and [YØCO]⁺ ions.