elektrophiles

Electrophiles, sometimes referred to as Elektrophile in German, are electron-deficient chemical species that seek electron density from nucleophiles. In the Lewis acid–base framework, an electrophile accepts an electron pair. They include cations such as H+, NO2+, and carbocations; as well as neutral molecules with polarized bonds, like the carbonyl carbon in aldehydes and ketones; and metal-containing Lewis acids such as BF3, AlCl3, and FeCl3.

Electrophiles participate in a range of reaction types. In electrophilic addition, an electrophile attacks a double bond, generating a carbocation that is then trapped by a nucleophile. In electrophilic aromatic substitution, an electron-rich arene reacts with a strong electrophile (for example, NO2+ or a sulfonium/acylium-type species) to form a substituted aromatic product. Nitration of benzene and halogenation of arenes are classic examples. In Friedel–Crafts reactions, generated acylium or alkyl cations act as electrophiles to form substituted arenes.

The reactivity of electrophiles is often described by hard–soft acid–base (HSAB) theory. Hard electrophiles, such as H+ or NO2+, are small and highly charged, whereas soft electrophiles are more polarizable, like certain halogen species or stabilized carbocations. The nature of an electrophile determines its selectivity, regioselectivity, and the conditions required for its generation.

Overall, electrophiles are a central concept in organic, inorganic, and organometallic chemistry, governing how substrates are activated and how bonds are formed through electron-pair acceptance from nucleophiles.