Chapter 16.4, Problem 10P

Interpretation Introduction

Interpretation:

The observation that Friedel-Crafts alkylations often give polysubstituted products but Friedel-Crafts acylations do not is to be explained.

Concept introduction:

Friedal-Crafts reaction is an electrophilic substitution reaction in which an aromatic compound reacts with an alkyl chloride or acyl chloride in the presence of AlCl₃ to yield an alkylbenzene or ketones. During Friedal-Crafts alkylation polyalkylated products are produced since the alkyl group which enters into the benzene ring are electron releasing and hence activates the ring towards further substitution. In acylation reaction such a situation does not arise as in the product acylbenzene an electron withdrawing and deactivating carbonyl group gets attached to the benzene ring. The acyl benzene thus becomes less reactive than unacylated starting material.

To explain:

The observations that Friedel-Crafts alkylation reactions give polysubstituted products but Friedel-Crafts acylations do not.