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

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–C 6 H 4 –NHCOR (X = NH, S, O; R = CF 3 , C 2 F 5 , C 3 F 7 ). 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 exact mass measurements and linked scan experiments. The proposed mechanism 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. Published in 2010 by John Wiley & Sons, Ltd.