Charge-remote and charge-proximate fragmentations in deuterium-labeled n-hexadecyltriphenylphosphonium cations upon high-energy collisional activation:: evidence for the involvement of a phenyl biradical

The charge-remote fragmentation mechanism for n-alkyltriphenylphosphonium cations was examined through the use of high-energy collision-induced dissociation experiments on specifically deuterium-labeled isotopomers. In addition to the study of the charge-remote fragmentation mechanism other ions in the spectra, formed by so-called charge-proximate fragmentations, have also been studied. It was found that different processes are responsible for the formation of the ions in the spectra. A deuterium-hydrogen isotope effect of approximately 2 was measured for the 3,3-H-2(2) and 9,9-H-2(2) isotopomers, indicating that a C-H cleavage is a rate-determining step in the formation of corresponding charge-remote product ions as was reported for alkali-cationized fatty acid esters. Substantial insertion of hydrogens from the triphenylphosphine moiety into the fully labeled alkyl chain upon high-energy collision-induced dissociation points to the involvement of an excited state biradical in the processes which take place upon high-energy collision-induced dissociation. (C) 1999 Elsevier Science B.V.