Unique para-effect in electron ionization mass spectra of bis(perfluoroacyl) derivatives of bifunctional aminobenzenes

Article abstract of DOI:10.1002/rcm.4661

A new kind of 'para-effect' under electron ionization (EI) conditions has been discovered for a series of bis(perfluoroacyl) derivatives of o-, m- and p-phenylenediamines, -hydroxybenzeneamines and -mercaptobenzeneamines of a common structure RCOX-C₆H₄-NHCOR (X=NH, S, O; R=CF₃, C₂F₅, C₃F₇). Only the para-isomers showed successive loss of a radical RCO^? and a molecule RCN, leading to very intense peaks in the EI spectra. The composition and the origin of the [M-COR-NCR]⁺ ions were confirmed by exactmassmeasurements and linked scan experiments. The proposedmechanism of their formation takes into account likely para-quinoid structures of the precursor ions. A similar rearrangement has not been observed for para-isomers in the series of bis(perfluoroacyl) derivatives of benzenediols, mercaptophenols and dimercaptobenzenes.