Question

what are Ipso substitution.

Answer 1

Ipso substitution: Substitution of an aromatic ring substituent (i.e., an attachment other than hydrogen). The mechanism is usually nucleophilic aromaticsubstitution, but ipso substitutionby an electrophilic aromaticsubstitution mechanism is also possible.

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Answer 2

The Ipso substitution is a special case of electrophilic aromatic substitution where the leaving group is not hydrogen. A classic example is the reaction of salicylic acid with a mixture of nitric and sulfuric acid to form picric acid. The nitration of the 2 position involves the loss of CO2 as the leaving group. Desulfonation in which a sulfonyl group is substituted by a proton is a common example. See also Hayashi rearrangement. In aromatics substituted by silicon, the silicon reacts by ipso substitution.