Ipso aromatic alkylation in the gas phase. Intermediacy and structure of gaseous heptaalkylbenzenium ions

The structure of heptaalkylbenzenium ions has been investigated in the gas phase with complementary techniques, i.e., chemical ionization mass spectrometry, alkylation of hexaalkylbenzenes by radiolytically generated cations, and collisionally induced dissociation mass spectrometry. The results allow us to assign the o-complex (Wheland intermediate) structure to the free, gaseous heptaalkylbenzenium ions, in agreement with the established structure of their salts in solution and in the solid state. The heptaalkylbenzenium ions represent the charged intermediates of the gas-phase “ipso”-substitution reactions, whose occurrence has been demonstrated and whose mechanism is briefly discussed.