Evidence of HF Loss in C or C ^– + C ₆ F _<i>x</i> H _{6– <i>x</i>} (1 ≤ <i>x</i> ≤ 5) Reactions

Patterns of anions produced by passing benzene and fluorobenzenes through a photoemission ion source show evidence of carbon addition with subsequent -H or HF loss. We recently reported a study of the fulvenallenyl structures of C₇F_<i>x</i>H_5-<i>x</i> ^- (0 ≤ <i>x</i> ≤ 2) formed in the former reaction. In this follow-up study, we report the anion PE spectra of the C₇F_<i>x</i>H_4-<i>x</i>^- (0 ≤ <i>x</i> ≤ 4) anions. We present experimental evidence that HF loss is necessary for C₇F_<i>x</i>H_4-<i>x</i>^- (0 ≤ <i>x</i> ≤ 4) formation, and calculations predict the reactions to be thermodynamically favorable. Based on a comparison between the experimental spectra and computational results on the anion and neutral, we conclude that two distinct C₇F_<i>x</i>H_4-<i>x</i>^- structures are formed. One structure resembles a fulvenallenyl structure that has undergone deprotonation from the acetylenic group, and the other is a cumulenic or other chain structure. The former is more stable than the latter except in the case of C₇F₄^-. Results of calculations suggest that the cumulenic structure becomes increasingly stable with fluorination.