Elektrophils

Elektrophils, commonly spelled electrophiles, are chemical species that seek electrons to form chemical bonds. In Lewis acid–base theory, an electrophile is an electron-pair acceptor. They are typically electron-poor, bear a positive charge, or possess a polarized bond that creates a partial positive center that attracts nucleophiles.

Common examples include protons (H+), carbocations (R3C+), and positively charged metal complexes. Neutral molecules can also act as electrophiles when they can accept electron density, for example nitronium ion NO2+ and the acylium ion RCO+. In halogenation, Br2 acts as an electrophile by generating a bromonium intermediate; in nitration of arenes, the nitronium ion NO2+ is the electrophile.

Electrophiles react with nucleophiles, which donate electron density to form covalent bonds. Many reactions proceed via a transition state where the electrophile bonds to the nucleophile. Typical reaction patterns include electrophilic aromatic substitution (such as nitration or sulfonation of benzene), electrophilic addition to alkenes and alkynes, acylations and alkylations in carbonyl and related chemistry, and certain polymerization mechanisms.

Hard and soft electrophiles (HSAB theory) describe preferences for nucleophiles of matching character, influencing selectivity and outcome. In synthesis, electrophiles are often generated in situ by reagents such as Lewis acids that activate a substrate to form a reactive electrophilic species.