Notice that the three players in a nucleophilic substitution reaction - the nucleophile, the electrophile, and the leaving group - correspond conceptually to the three players in an acid-base reaction...Notice that the three players in a nucleophilic substitution reaction - the nucleophile, the electrophile, and the leaving group - correspond conceptually to the three players in an acid-base reaction: the base, the acidic proton, and the conjugate base of the acid, respectively.