GAS-PHASE REACTIONS OF CARBON CLUSTER IONS WITH ISOMERIC CHLOROPROPENES

Gas-phase ion/molecule reactions of carbon cluster ions (C-n(.+), n = 10-20) with allylchloride (AC) and 2-chloro-propene (CP) were investigated by Fourier transform ion cyclotron resonance spectrometry (FT-ICR). The carbon cluster ions C-n(.+) were generated by electron impact ionization of perchloroarenes and subsequent elimination of all Cl substituents from the molecular ion giving rise to monocyclic C-n(.+). Clear pseudo-first-order reactions were observed for the carbon cluster ions C-n(.+) thus formed without any sign of isomeric clusters of different reactivity. An exception is C-11(.+), for which a small amount of unreactive ions was observed. The reactions of C-n(.+) with AC and CP at low operating pressure (1.2 x 10(-8)-8.0 x 10(-7) mbar) yield product ions Cn+3H5+ by loss of Cl from an intermediate adduct. Rate constants for the reactions with CP are always distinctly larger than with AC in spite of the smaller dissociation energy of the C-Cl bond in AC. Exceptionally large reaction efficiencies are found for C-13(.+) and C-17(.+), corroborating the high reactivity of cyclic anti-aromatic C-n(.+) with n = 4r + 1. The nature of the reaction products depends on the number of carbon atoms in C-n(.+). Secondary reactions of primary product ions Cn+3H5+ were observed only for reactions of odd numbered C-13(.+) and C-17(.+). Further, on collision induced dissociation (CID) the product ions from even C-n(.+) yield exclusively C3H3+, while product ions from odd C-n(.+) generate several fragment ions by loss of H and of C-(2-4)H-2. A reaction model explaining these observations is proposed.