Charge inversion as a structural probe for C6H5+ and C6H6+. cations

Charge reversal (+CR-) of cations to anions can be used to structurally dif ferentiate isomeric C6H5+ and C6H6+. hydrocarbon ions by means of tandem ma ss spectrometry. In view of the manifold of possible isomers, only a few pr ototype precursors are examined. Thus, charge inversion demonstrates that e lectron ionization of 2,4-hexadiyne yields an intact molecular ion, whereas the charge inversion spectra of C6H6+. obtained from benzene, 1,5-hexadiyn e, and fulvene are identical within experimental error. Similarly, the +CR- spectrum of the C6H5+ cation generated by dissociative ionization of 2,4-h exadiyne is significantly different from the +CR- spectrum of C6H5+ obtaine d from iodobenzene, suggesting the formation of a 2,4-hexadiynyl cation fro m the former precursor. Although charge inversion of cations to anions has a low efficiency and requires large precursor ion fluxes, the particular va lue of this method is that the spectra may not just differ in fragment ion intensities, but these differences can directly be related to the underlyin g ion structures. (J Am Soc Mass Spectrom 1999, 10, 878-882) (C) 1999 Ameri can Society for Mass Spectrometry.