A new kind of "para-effect" under EI conditions has been discovered for a series of bis(perfluoroacyl) derivatives of o-, m- and p- phenylendiamines, hydroxybenzeneamines and mercaptobenzeneamines of a common structure RCOX C6H4 NHCOR (X = NH, S, O; R = CF3, C2F5, C3F7). Only para-isomers showed successive loss of radical RCO and 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.
Citation: Rapid Communications in Mass Spectrometry
Pub Type: Journals
bifunctional benzenes, bis(perfluoroacyl) derivatives, electron ionization mass spectra, para-effect