Elektrofil

An electrophile, from the Greek for “bearing affinity for electrons,” is a chemical species that seeks electrons. In Lewis acid–base theory it is an electron-pair acceptor (a Lewis acid). Electrophiles are typically electron-poor or positively polarized, and they react by forming a covalent bond with a nucleophile, which donates an electron pair.

Common electrophiles include cations such as H+ and carbocations; positively polarized atoms in polar bonds, for example the carbonyl carbon in aldehydes and ketones, or the iminium carbon; and neutral Lewis acids such as boron trifluoride (BF3), aluminum trichloride (AlCl3), and sulfur trioxide (SO3). Polarizable substrates like alkyl halides under certain conditions (such as SN1) or alkenes in electrophilic addition reactions also function as electrophiles.

Mechanistically, an electrophile accepts an electron pair from a nucleophile, forming a new covalent bond. The rate and outcome of the reaction depend on the electrophile’s readiness to accept electrons; more electron-deficient centers are generally more reactive. Factors such as substituents, solvent polarity, and the ability of the molecule to stabilize additional charge influence electrophilicity.

In organic synthesis, electrophiles are used to install new functional groups, activate substrates, or generate reactive intermediates. In biochemistry, electrophiles can modify nucleophilic sites on biomolecules, which may contribute to signaling, regulation, or toxicity. Electrophilicity is related to Lewis acidity and related indices and is contrasted with nucleophilicity, the tendency to donate electrons.