When 5 -phenylpent- 1 -ene is heated in the presence of a catalytic amount of a strong acid, it undergoes an intramolecular reaction. The major organic product formed is:

Step-by-step solution

Protonation of the terminal double bond of 5 -phenylpent- 1 -ene by the acid catalyst follows Markovnikov's rule, yielding a secondary carbocation at C 2 of the pentyl chain. The tethered benzene ring acts as an internal nucleophile, attacking this carbocation via an intramolecular electrophilic aromatic substitution (Friedel-Crafts alkylation). The attack from the ortho position of the benzene ring onto the C 2 carbocation forms a stable 6 -membered saturated ring fused to the benzene ring. The methyl group ( C 1