Mechanism Step 1:Attack on the electrophile forms the sigma complex. H H H H H H〈 H《 E+ H H H sigma complex (arenium ion) Step 2:Loss of a proton gives the substitution product. H H H base: +base-H H H H H > Copyright 2005 Pearson Prentice Hall,Inc. Chapter 17 3Chapter 17 3 Mechanism Step 1: Attack on the electrophile forms the sigma complex. => Step 2: Loss of a proton gives the substitution product