Question

Explain why Friedel-Crafts alkylations often give polysubstitution but Friedel-Crafts acylates do not.

CH3 CH3 снасі AICI: + H3C (Product mixture) che LICHE CCH3 CH3CCI AICI: (Sole product)

Answer 1

Ang- Friedel-Craft afkylation :- During these reaction, aky le group is attached to benzene ring. As we know, alkyl group is electron donating group, hence carbocation formed during intermediate step can travell throughout ring, hence there is a chance of poly substitution of alkyl group. H. CH₂ + Ancie сне "Alcз CH3 H CH₂ CH3 Hg CH3 4 fauces CH3 Chcet CH₃Cd AlCl3 CH3 here-CHg group, activates the benzene sing at para position , hence again akylation takes place.)

(6 Frieded craft As we aly lution in know, Alyle group is deactivationg hence, when acylation takes place it deactivates benzene ring hence no further aculation takes place. 0-C-CH3 Lot :44 + лАХИ, (CH3 + Al lla C-CH₂ +HCl +40С (since the -(-CH₂ , is an electron withdrawing group hence it deactivates benzene sing for further acylation because there is a nigh (tive charge density created in benzene ring.)