Mass spectrometry in structural and stereochemical problems—CC A study of the fragmentation processes of some pyrilium salts

The principal mode of fragmentation, at both 70 and 15 eV, of pyrilium iodides (I to V) which are substituted by at least one methyl group is the elimination of hydrogen iodide from the non-detectable molecular ion. In contrast the mass spectrum (Fig. 6) of 2,4,6-triphenyl pyrilium iodide (VI) shows its dominant fragmentation to be due to the loss of an iodine atom from the molecular ion. The mass spectra (for example Figs. 6 and 7) of 2,4,6-triphenyl pyrilium iodide, bromide and tetrafluoroborate (VI, VII and VIII) are virtually identical except for the peaks corresponding to a molecule of iodine (m/e 254), hydrogen iodide (m/e 128) and iodine (m/e 127) in the mass spectrum (Fig. 6) of the iodide. Other fragmentation routes common to these pyrilium salts are described.