Formation and stability of gaseous tolyl ions

Collisional activation mass spectra confirm that tolyl ions can be produced from a variety of CH₃C₆H₄Y compounds. High purity o-, m- and p-tolyl ions are prepared by chemical ionization of the corresponding fluorides (Y=F) as proposed by Harrison. In electron ionization of CH₃C₆H₄Y formation of the more stable tropylium and benzyl ionic isomers usually accompanies that of the o-, m- and p-tolyl ions. Isomerization of low energy CH₃C₆H₄Y]⁺? to Y–methylenecyclohexadiene]⁺? is proposed to account for most benzyl]⁺ formation, while the tropylium ion appears to arise from the isomerization of tolyl ions formed with higher internal energies, o-, m-, p-tolyl]⁺→ benzyl]⁺→ tropylium]⁺, consistent with Dewar's predictions from MINDO/3 calculations.