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, C(6)H(6)(.+), 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, C(4)H(4)(.+), and m/z 39, C(3)H(3)(+). Isotopic labeling studies show that C(4)H(4)(.+) and C(3)H(3)(+) are formed with nearly statistical hydrogen incorporation, indicating a complex mechanism that scrambles all protons.