Rearrangement processes of negative ions in the gas phase: [M Hal]− ions in halogenated azobenzenes. Resonance stabilization of negative ions

Ionization efficiency curves for [M  X]− ions from p‐XC6H4NNC6H5 molecules (XF, Cl, Br) have been registered in the energy range 0–9 eV with appearance energies 3.3, 4.1 and 3.2 ± 0.2 eV, respectively. The heats of formation of 17 isomeric C12H9N− ions have been estimated using isodesmic reactions. The possible mechanism of isomerization of molecule ions leading to various isomeric [M  X]− ions is represented. The resonance stabilization of both negative and positive ions, questioned for negative ions by some workers, was confirmed by measuring appearance energies of conjugated ions [M  H]− and [M  (CCl2 + CI)]− or [M  Me]+ and [M  CCl3]+ coming from p‐MeC6H4OR (R or Me) and 4‐Methyl‐4‐trichloromethylcyclohexa‐2,5‐dienone, respectively.