Structures of the C8H6+Cation Formed upon Loss of Acetylene from Ionized Naphthalene

Ionized naphthalene undergoes unimolecular loss of acetylene in the gas phase, which leads to the formation of a C 8 H 6 + species of hitherto unknown structures. In order to possibly afford different isomers, C 8 H 6 + is generated using several precursors, i.e., naphthalene, azulene, 1-chlorobenzocyclobutene, benzocyclobuten-1-ol, 1,2-di(bromomethyl)benzene, phenylacetylene, 2,4,6-octatriyne, 2,7-dichloro-3,5-octadiyne, and 1,3,5,7-cyclooctatetraene. Mass-selected C 8 H 6 + ions are investigated by different mass spectrometric techniques, such as collisional activation (CA), neutralization reionization (NR), and charge reversal (CR). Charge reversal of cations to anions is most informative and yields structurally indicative fragmentations, which are much less pronounced with the other techniques. Comparison of the CR spectra of the C 8 H 6 + cations disputes the formation of ionized phenylacetylene and 2,4,6-octatriyne upon loss of acetylene from naphthalene ion. Further, formation of ionized cycloocta-1,3,5-triene-7-yne can be ruled out by comparison with the data obtained for the corresponding anionic species. While the experimental results are in accord with the formation of ionized benzocyclobutadiene upon loss of acetylene from naphthalene ion, other isomers which have not been considered previously may also represent likely candidates.