The mass spectra of carboxylic acids—III: The structures of molecular and fragment ions in benzoic acid and related molecules

The mass spectra of benzoic acid and its carboxyl-deuterated derivative have been studied in detail. Molecular and fragment ion structures are proposed and the role of ortho hydrogen atoms in rearrangements is discussed. The behaviour under electron-impact of phthalaldehydic acid and its carboxyl deuterated derivative provides evidence in support of ion structures in the benzoic acid fragmentation. From these results the fragmentation mechanism for phthalic acid is further elucidated. The mass spectrum and fragmentation mechanism of thiobenzoic acid is described and compared with that of benzoic acid.