what is nucleophilic reaction
S N 2). Nucleophilic substitution is the reaction of an electron pair donor (the nucleophile, Nu) with an electron pair acceptor (the electrophile). An sp 3 -hybridized electrophile must have a leaving group (X) in order for the reaction to take place.ince the nucleophile is free to attack from either side, this reaction is associated with racemization. In both reactions, the nucleophile competes with the leaving group. Because of this, one must realize what properties a leaving group should have, and what constitutes a good nucleophile.