280REACTIONS OF ARENES: ELECTROPHILIC AROMATIC SUBSTITUTION12.3The aromatic ring of 1,2,4,5-tetramethylbenzene has two equivalent hydrogen substituents. Sul-fonation of the ring leads to replacement of one of them by @SO3H.12.4The major product is isopropylbenzene.Aluminum chloride coordinates with 1-chloropropane to give a Lewis acid/Lewis base complex,which can be attacked by benzene to yield propylbenzene or can undergo an intramolecular hydrideshift to produce isopropyl cation. Isopropylbenzene arises by reaction of isopropyl cation withbenzene.12.5The species that attacks the benzene ring is cyclohexyl cation, formed by protonation ofcyclohexene.The mechanism for the reaction of cyclohexyl cation with benzene is analogous to the general mech-anism for electrophilic aromatic substitution.12.6The preparation of cyclohexylbenzene from cyclohexene and benzene was described in text Sec-
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