Substituent effects in the mass spectra of benzoyl hetarenes

The mass spectra of several benzoyl hetarenes, of 2‐benzoyl pyridines substituted at the phenyl and pyridyl group, respectively, and of phenyl substituted 2‐benzoyl pyrroles, have been studied with respect to the formation of benzoyl and hetaroyl ions. A correlation between the intensity of benzoyl ions, relative to molecular ion intensity, and the π‐electron density at the substituted carbon atom of the hetarene has been observed for benzoyl hetarenes. The relative intensities of (substituted) benzoyl ions of substituted 2‐benzoyl pyridines and 2‐benzoyl pyrroles are not easily related to substituent constants of Hammett equations. The relative ionization energies of phenyl substituted 2‐benzoyl pyridines, however, and the relative appearance energies of substituted benzoyl ions derived therefrom follow the σ IP + ‐constant of Bentley and Johnstone and the σ + ‐constants of Brown, respectively.