The reactivity of the (phenyl)Cr(CO)(3)-substituted alpha-propargyl cation 2 was quantified by measuring the kinetics of nucleophilic trapping reactions. In comparison to related dicobalthexacarbonyl alkynyl substituted carbenium ions the electiophilicity E of 2 is by 2.5 orders of magnitude larger and, thus, this species is more reactive. (C) 2000 Elsevier Science Ltd. All rights reserved.