HYPERVALENT PYRROLIDINIUM RADICALS BY NEUTRALIZATION-REIONIZATION MASS-SPECTROMETRY - METASTABILITY AND RADICAL LEAVING GROUP ABILITIES

Neutralization-reionization mass spectrometry was used to generate hyp ervalent radicals pyrrolidinium (1H(.)), N-methylpyrrolidinium (2H(.)) , N-ethylpyrrolidinium (3H(.)), N-phenylpyrrolidinium (4H(.)), N,N-dim ethylpyrrolidinium (5.), N-methyl-N-ethylpyrrolidinium (6.), and their deuterium-labeled derivatives and to study their dissociations in the gas phase. Isotopomers of pyrrolidinium and N-phenylpyrrolidinium sho wed small fractions of stable radicals of microsecond Lifetimes that w ere detected following collisional reionization. The leaving group abi lities in radical dissociations were established as H-. much greater t han C2H5. approximate to C6H5. > CH5.. The hydrogen atom was the best leaving group in secondary and tertiary pyrrolidinium radicals 1H(.)-4 H(.), whereas losses of ethyl, phenyl, and ring openings by N-C bond c leavages were less facile. Methyl was the worst leaving group among th ose studied. Ring cleavages dominated the dissociations of quaternary pyrrolidinium radicals 5. and 6., whereas losses of alkyl substituents were less efficient. The electronic properties of hypervalent ammoniu m radicals are discussed to rationalize the experimental leaving group abilities of hydrogen atom, alkyl, and phenyl radicals. (C) 1998 Amer ican Society for Mass Spectrometry.