The nature of the blue species formed when 1,1-diphenylethylene chemisorbs and reacts on acidic solids

The blue species obtained when 1,1-diphenylethylene chemisorbs on highly acidic solids arises from a very minor dimerization reaction where a less stable canonical form of the initial carbenium ion adds to Φ₂C=CH₂ (Φ=phenyl). Proton loss followed by H^- ion abstraction from the resulting olefin then affords a highly conjugated ion as the blue species. This revised version was published online in July 2006 with corrections to the Cover Date.