Question

poly alkylation of benzene ring is possible but poly acylation is not possible. explain

Answer 1

There are possibilities of carbocation rearrangements when you are trying to add a carbon chain greater than two carbons. The rearrangements occur due to hydride shifts and methyl shifts. For example, the product of a Friedel-Crafts Alkylation will show an iso rearrangement when adding a three carbon chain as a substituent.  the reaction will only work if the ring you are adding a substituent to is not deactivated. substituents that activate or deactivate a benzene ring, Activating and Deactivating Benzene Rings One way to resolve these problems is through Friedel-Crafts Acylation.