The mass spectra of nitrophenyl(phenyl)methanes: the formation of an M–17 ion from the meta- and para-isomers

The mass spectra of all three nitrophenyl(phenyl)methanes (nitrodiphenylmethanes) show an M–OH species produced directly from the molecular ion. In the case of the 2-isomer this arises almost entirely by the expected interaction between the ortho-substituents. Deuterium labelling shows that, for the 4-isomer, the hydrogen atom lost in the hydroxyl radical originates primarily in the aromatic ring bearing the nitro-substituent and a mechanism is suggested to account for this. The formation of the M–17 ion may be followed by loss of a second hydroxy-group. Discrepancies in the conclusions drawn from a study of the molecular ion region of two deuteriated analogues of 2-nitrodiphenylmethane highlight the danger of relying on evidence from the spectrum of a single labelled compound to confirm a suspected fragmentation mode. The mass spectra of some related compounds are also discussed.