Chapter 19.6, Problem 10CC

Interpretation Introduction

Interpretation:

The mechanism for the following reaction has to be illustrated –

                  

Concept Introduction:

Friedel Crafts reaction is an electrophilic substitution reaction. This reaction is useful to introduce alkyl, aryl or acyl group onto benzene ring. So this reaction is commonly known as Friedel Crafts acylation if acyl group is imparted on benzene ring or Friedel Crafts alkylation if alkyl group is imparted on benzene ring.

Benzene is highly stable that the sole presence of any alkyl or acyl halide is not enough to initiate the reaction. A catalyst, preferably a Lewis acid such as ${\text{AlCl}}_{\text{3,}}{\text{FeCl}}_{\text{3}}\text{,}{\text{BF}}_{\text{3}}\text{etc}$ is required to initiate the reaction. The Lewis acid catalyst assists in the formation of electrophile. Alkyl halide reacts with Lewis acid to generate alkyl ion as electrophile. With acyl halide acylium ion is formed as electrophile. The electrophile is attacked by pi electrons of benzene and a sigma complex is formed as a result of resonance. The sigma complex is converted to alkyl or acyl benzene which is the end product.

Aromaticity is the property of organic compounds having cyclic and planar structure with $\left(\text{4n+2}\right)\text{π}$ electrons. It attributes to the stability of the compound. A compound that is aromatic is said to be highly stable. Benzene is an aromatic compound and the substitution reactions of benzene are known as aromatic electrophilic substitution reactions.