The negative-ion mass
spectra of 3- and 4-nitrophthalic anhydride contain a series of rearrangement
ions. One of these, an M-CO2 ion, is mainly produced by loss of CO
from the anhydride unit together with an oxygen of the nitro group.
The three nitrophenyltrifluoroacetamides are readily differentiated
by negative-ion mass spectrometry. Many unusual fragmentations are noted in
these spectra and certain of these have been substantiated by labelling and
defocusing studies.