Definitive characterization of some C5H5N.+ and C6H7N.+ radical cations byassociative 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 secto r 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 o f the four substrates as the latter C5H5N.+ ion exhibits a radical-type rea ctivity 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-merhyl-2-dehydropyridine radical cation, is realized when all of the above substrates are used in the analysis. (Int J Mass Spectrom 206 (2001) 91-103) (C) 2001 Elsevier Science B.V.