In a nucleophilic substitution reaction, what role does a nucleophile play?

In a nucleophilic substitution reaction, the nucleophile is crucial as it donates an electron pair to form a new covalent bond with the electrophile, typically a carbon atom that is part of a leaving group. This process initiates the substitution of the leaving group with the nucleophile.

Nucleophiles are characterized by their electron-rich nature, meaning they have a pair of electrons that can be shared or donated. When they approach a molecule containing a good leaving group, they can effectively bond with the carbon atom, replacing the leaving group and resulting in a new compound. This donation of an electron pair is fundamental to the mechanism of nucleophilic substitution, as it leads to the transformation of reactants into products through the formation of new bonds.

Other options describe different roles in chemical reactions. For instance, electron pair acceptors are known as electrophiles, catalysts speed up reactions without being consumed, and stabilizing products generally pertains to other interactions in the chemical process but do not define the function of a nucleophile in this context.