Alkenyl Benzene

Alkenyl benzenes contain a double bond in the side chain of benzene ring e.g.   

These compounds are prepared as follows:

The reactivity of the double bond is greater than the benzene towards electrophilic reagents. Thus mild conditions are required for the addition reaction across the double bond as compared to those required for the benzene ring.

First step is the formation of carbocation or free radical.

The higher stability of benzyl cation or radical relative to the conjugated alkenyl benzene makes the latter more reactive than simple alkenes.

In the presence of peroxides, the reaction taking place is (peroxide effect) as follows.