nucleophileelectrophile

Nucleophile–electrophile is a general way to describe the core donor–acceptor interactions that drive many chemical reactions. A nucleophile is a species that donates an electron pair to form a bond, often carrying a lone pair, negative charge, or π electrons. An electrophile is an electron pair acceptor, typically electron-poor or polarized to create an electron-deficient center that can accept electron density.

In many processes, a nucleophile attacks an electrophilic center, leading to bond formation and a change in molecular connectivity. Nucleophilicity and electrophilicity are influenced by factors such as charge, polarizability, steric hindrance, and solvent. Common nucleophiles include hydroxide, cyanide, amines, alkoxides, and thiolates; common electrophilic centers include carbonyl carbons in aldehydes and ketones, and carbon atoms bearing leaving groups in alkyl halides. Electrophilicity can be enhanced by nearby electron-withdrawing groups or by developing a positive charge during the reaction.

The hard–soft acid–base (HSAB) framework helps predict interactions: hard nucleophiles tend to attack hard electrophiles, while soft nucleophiles favor soft electrophiles. Frontier molecular orbital theory describes reactivity in terms of HOMO (nucleophile) and LUMO (electrophile) energy alignment, providing a qualitative basis for reaction rates and selectivity.

Common contexts include nucleophilic substitution (SN1, SN2), nucleophilic additions to carbonyls, and ring-opening or opening of strained systems such as epoxides. Solvent choice can modulate nucleophilicity; polar aprotic solvents often enhance SN2 reactions, while protic solvents can stabilize charged nucleophiles and reduce their reactivity.

Overall, the nucleophile–electrophile concept underpins much of synthetic planning, mechanism analysis, and the design of chemical transformations.