CH₂⁺ transfer to pyridine nucleophiles: a means of producing α-distonic ions

The distonic radical cation C₅H₅N⁺-^·CH₂ can be generated by the reactions of neutral pyridine with the radical cations of cyclopropane, ethylene oxide, and ketene, as well as with the [C₃H₆]⁺ ion from fragmentation of tetrahydrofuran. The distonic product ion can be distinguished from isomeric methylpyridine radical cations because the former gives characteristic [M-CH₂]⁺, [M - CH₂NCH]⁺, and a doubly charged ion, all of which are produced on collisional activation. Furthermore, the distonic species completely transfers CH₂⁺ to more nucleophilic, substituted pyridines. These properties are all consistent with the assigned distonic structure. Another distonic isomer, the (3-methylene) pyridinium ion, can be distinguished from the (1-methylene)pyridinium ion on the basis of their different fragmentation behaviors. The latter ion exhibits higher stability (lower reactivity) than the prototypal [·CH₂NH₃⁺], making available a distonic species whose bimolecular reactivity can be readily investigated.