Reactions of diacetylene radical cation with ethylene

Ion-molecule reactions and energy-resolved mass spectrometry have been used to determine the structures of the products formed in the reaction of diacetylene radical cation with ethylene in a flowing afterglow-triple quadrupole instrument. The structure of the adduct ion, C6H6·+, has been determined to be that of singly ionized benzene. The reaction thus presents a first example of the ability of diacetylene radical cation to undergo an aromatic ring forming reaction. The other products formed in the reaction are m/z 52, C4H4·+, and m/z 39, C3H3+. Isotopic labeling studies show that C4H4·+ and C3H3+ are formed with nearly statistical hydrogen incorporation, indicating a complex mechanism that scrambles all protons. [Copyright &y& Elsevier]