Heterolytic reaction in which the entering group adds to a nucleophile and in which the leaving group, or electrofuge, relinquishes both electrons to its reaction partner, whereupon it becomes another potential electrophile.

Example: Azo coupling: \[\begin{align} \ce{RN2^{+} + H2NC6H5 -> \textit{p}\!\;{-}H2NC6H4N=NR + H^{+}}\\ \small \rm{(electrophile) \qquad (nucleophile) \quad\quad\quad \quad(electrofuge)\qquad\qquad \quad}\end{align}\]

Note: It is arbitrary to emphasize the electrophile and ignore the feature that this is also a nucleophilic substitution, but the distinction depends on the electrophilic nature of the reactant that is considered to react with the substrate.