Electrophilic Aromatic Substitution E H H B-H attack on an electrophile sigma complex substituted Copyright2010 Pearson Prentice Hall,Inc. Although benzene's pi electrons are in a stable aromatic system,they are available to attack a strong electrophile to give a carbocation. This resonance-stabilized carbocation is called a sigma complex because the electrophile is joined to the benzene ring by a new sigma bond. Aromaticity is regained by loss of a proton. Chapter 17 2 Chapter 17 2 Electrophilic Aromatic Substitution ▪ Although benzene’s pi electrons are in a stable aromatic system, they are available to attack a strong electrophile to give a carbocation. ▪ This resonance-stabilized carbocation is called a sigma complex because the electrophile is joined to the benzene ring by a new sigma bond. ▪ Aromaticity is regained by loss of a proton