Mechanism of the Gas-Phase Reaction of the Benzene Radical Cation and Various Alkyl Iodides

The gas-phase reaction of the benzene radical cation with 2-iodoalkanes was explored by using tandem mass spectrometry (mass spectrometry/mass spectrometry) and pulsed ion cyclotron resonance spectrometry. The nature of the reaction products was determined from their collision-induced dissociation spectra. It was found that the benzene radical cation reacts with the 2-iodoalkanes under collisional stabilizing conditions to form an observable collision complex or intermediate. The intermediate undergoes reductive elimination of an iodine radical to yield a hydrocarbon cation of the “Wheland intermediate” type. Specifically, the product of the reaction of C₆H₆ radical cation and 2-iodopropane was shown to have the same CID spectrum and, thus, the same structure as protonated isopropylbenzene or isopropylated benzene. The reaction of C₆H₆⁺. with 2-iodobutane similarly produces protonated isobutylbenzene or isobutylated benzene.