C₂H₂ trimerion = benzene

Over the years, physical chemists have seen tantalizing indications that, when ionized acetylene clusters are produced in the gas phase, acetylene trimer ions-(C₂H₂)₃⁺-can form new covalent bonds to yield the benzene cation (C₆H₆⁺). Now, M. Samy El-Shall and coworkers at Virginia Commonwealth University have provided the most conclusive evidence for the formation of benzene ions from the largest ionized acetylene clusters ever reported (J. Am. Chem. Soc., DOI: 10.1021/ja064405g). Using a combination of mass-selected ion mobility and fragmentation data, along with theoretical calculations, the team concludes that (C₂H₂)₃⁺ "structurally looks like benzene, it has stability similar to that of benzene, it fragments like benzene, therefore, it must be benzene!" Formation of the benzene cation from ionized acetylene may be the first step in the formation of polycyclic aromatic hydrocarbons (PAHs) that have been spectroscopically observed in space, El-Shall tells C&EN. Benzene has been postulated to be the "missing link" between simple carbon molecules like acetylene and complex molecules like PAHs.