electrophil

An electrophile is a chemical species that accepts electron density from a nucleophile. In Lewis acid–base terms, an electrophile is a Lewis acid, possessing an empty orbital or a positively charged center that can accept an electron pair from a Lewis base. Electrophiles are often electron-poor and seek electron density to form a bond, making them central players in many reaction types.

In organic chemistry, electrophiles react with nucleophiles to form new covalent bonds. They are key in electrophilic addition to alkenes, where a proton or other electrophile adds to the double bond to generate a carbocation intermediate that is then attacked by a nucleophile. They also drive electrophilic aromatic substitution, in which a positively charged electrophile such as a nitronium ion NO2+ or sulfur trioxide reacts with an activated aromatic ring, followed by deprotonation to restore aromaticity. Carbonyl compounds are common electrophiles as well, with the carbonyl carbon of aldehydes, ketones, and acyl chlorides being susceptible to attack by nucleophiles.

Common examples of electrophiles include protons (H+), carbocations, the nitronium ion NO2+, sulfur trioxide (SO3), boron trifluoride (BF3), aluminum trichloride (AlCl3), and highly activated carbonyl carbon in aldehydes, ketones, and acyl chlorides. In many reactions, the electrophile’s reactivity is modulated by substituents, solvent effects, and the presence of leaving groups, which influence the energetics of bond formation and subsequent steps.

Note: the standard term is electrophile; electrophil is a less common variant spelling.