Aromatic nitration at the encounter rate in the gas phase

In the title reaction, the formation of an “early complex,” the gas-phase analogue of the “encounter” pair in solution, is rate-determining above a certain activation of the arene (nitrating agent [RNO3H]⊕, R CH3, CF3CH2). This would also explain why the intermolecular selectivity between toluene and 1,2,3,5-tetramethylbenzene is small in this reaction, whereas the intramolecular selectivity in the case of benzylmesitylene 1 is large. In the latter case, 2 is formed preferentially.