Ortho effects–I: Fragmentation mechanisms in some ortho‐substituted nitroarenes

The mass spectra of o‐nitrobenzoic acid, o‐nitroanisole, o‐nitrosobenzoic acid, o‐nitrobenzamide, o‐nitrobenzyl alcohol and o‐nitrosobenzaldehyde have been studied. Fragmentation mechanisms are proposed for the above compounds; their elucidation was aided by isotopic labeling with D and O18. Two ‘ortho‐effects’ are discussed; one involving H atom transfer between substituents and the other migration of an atom or group to a charge carrying vacant ortho position. The importance of nitro to nitrite conversion in molecular and fragment ions is discussed.