ISSUE:

Hello good weekend!

I was checking the reactions of fridel crafts on benzene. Well, roughly speaking, I understand the great drawbacks that alkylation presents, mainly rearrangements and polysubstitutions.

But I was wondering what is the cause of polysubstitutions not occurring in acylation. That is, I understand that the rearrangement is a characteristic of the electrophile after the formation of the carbocation.

but in the polysubstitutions I do not understand why they cannot be given thinking that the substrate is "the same" benzene.

All the best!

Hello!
This is because the acyl groups introduced by acylation are strong deactivators and prevent the entry of a second acyl.
In fact, after putting an acetyl in benzene it is not possible to repeat the reaction given the low reactivity of the ring. On the contrary, the Friedl-Craft alkylation introduces carbon chains that are activating groups.

I wish you a good Saturday night!

Thank you so much! I later realized that the Fridel Crafts reaction only occurred in activated benzenes, once the acetyl is incorporated it is deactivated, but with alkylations, since they are activating groups, it can continue to react. Thank you!