Abstract: The loss of substituents (X= H, F, CH3, CI, Br, I) from the molecular ions of ortho- substituted l-phenyl-l-(2-pyridy1) ethylenes la-f and of the isomeric l-phenyl-l-(3-pyridyl)-and l-phenyl-l-(4-pyridyl) ethylenes 2 and 3 has been investigated. Cyclic fragment ions a are formed from the ortho-substituted l-phenyl-l-(2-pyridyl) ethylene molecular ions by an intramolecular aromatic substitution reaction. The energetic requirements of this reaction ...
