The attachment of an entering group to a position in an aromatic compound already carrying a substituent group (other than hydrogen). The entering group may displace that substituent group but may also itself be expelled or migrate to a different position in a subsequent step. The term "ipso-substitution" is not used, since it is synonymous with substitution.
For example:
where E+ is an electrophile and Z is a substituent (other than hydrogen). See also cine-substitution, tele-substitution.
