Gas-phase reactions of the 6-dehydroanilinium ion and its isomers

Article abstract of DOI:10.1002/jms.1190300113

Collisional activation of protonated 2-, 3- and 4-iodoanilines in a dual-cell Fourier transform ion cyclotron resonance spectrometer results in the loss of an iodine atom to yield product ions of m/z 93. Ion-molecule reactions and energy-resolved collision-activated dissociation experiments demonstrate that these three ions are structurally distinct, and that they are distonic ions. The ions were identified as the 2-, 3- and 4-dehydroanilinium ions, the high-energy distonic isomers of ionized aniline. The reactivity of these charged phenyl radicals is largely analogous to that of the phenyl radical. For example, the 4-dehydroanilinium ion abstracts an iodine atom from isopropyl iodide, a thiomethyl group from dimethyl disulfide, and adds to cyclohexene. Comparison of the collision-activated dissociation product abundances of the ion formed upon CH₃S abstraction to that of a reference ion suggests that bond formation occurs at the formal radical site upon CH₃S abstraction. Hence, the reaction probably occurs via a simple radical abstraction mechanism similar to that of the phenyl radical. However, some neutral reagents react with the charge site of the 4-dehydroaniliaium ion, and yet others undergo a two-step reaction sequence involving the charge site in addition to the radical site. For example, certain basic molecules induce isomerization of the 4-dehydroanilinium ion to the significantly more stable ionized aniline by deprotonating the charge site and then donating a hydrogen atom to the radical site.