Definitive characterization of some C5H5N·+ and C6H7N·+ radical cations by associative ion–molecule reactions

Isomeric C5H5N·+ and C6H7N·+ radical cations were allowed to interact with various neutral reagents in the quadrupole collision chamber of a six sector magnetic deflection type tandem mass spectrometer. Using CH3SSCH3, CH3OH, or H2O, iso-C3H7I, and tert-C4H9NC as substrates, specific associative ion–molecule reactions occur whose products were analyzed in a subsequent high energy collision induced dissociation experiment. Differentiation between ionized pyridine and its 1,2-H shift isomer is readily achieved with each of the four substrates as the latter C5H5N·+ ion exhibits a radical-type reactivity characteristic of its distonic character. An unambiguous structure characterization of the C6H7N·+ ions, namely ionized 2-methylpyridine, the N-methylene pyridinium ylide ion, the 2-methylene-1-hydropyridine ion, and the N-methyl-2-dehydropyridine radical cation, is realized when all of the above substrates are used in the analysis.