Electrophile
An electrophile is a chemical species that accepts an electron pair from a nucleophile to form a new covalent bond, acting as a Lewis acid. Electrophiles typically carry a full positive charge, a partial positive charge (δ+), or an empty orbital that makes them electron-deficient and reactive towards electron-rich species. Electrophilic attack is the first step in many important organic reactions, including electrophilic aromatic substitution, electrophilic addition to alkenes, and Friedel–Crafts reactions used in industrial chemistry.
Common Electrophiles in Organic Chemistry
| Electrophile | Formula | Source of Electrophilicity | Reaction Type | Example Product |
|---|---|---|---|---|
| Proton | H⁺ | Positive charge / empty 1s orbital | Protonation, acid catalysis | Oxonium ion, carbocation |
| Carbocation | R⁺ (R₃C⁺) | Positive charge, empty p orbital | SN1, E1, rearrangements | Substituted product |
| Bromine | Br₂ | Polarisation by alkene π system | Electrophilic addition | 1,2-Dibromide |
| Acylium ion | RCO⁺ | Positive charge on carbonyl carbon | Friedel–Crafts acylation | Aryl ketone |
| Carbonyl carbon | R–C(=O)–R' | δ+ charge from C=O polarisation | Nucleophilic addition | Alcohol |
| Lewis acid | AlCl₃, BF₃ | Empty orbital | Coordination, activation | Complex with Lewis base |
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Related Terms
Nucleophile
A nucleophile is a chemical species that donates an electron pair to an electrophile to form a new covalent bond, acting as a Lewis base. Nucleophiles are characterised by the presence of a lone pair of electrons, a negative charge, or a region of high electron density that attacks electron-deficient centres (electrophilic carbons). Strong nucleophiles drive SN2 reactions and nucleophilic addition; weaker nucleophiles favour SN1 pathways — making nucleophilicity a key parameter in predicting organic reaction outcomes.
Addition Reaction
An addition reaction is a chemical reaction in which two or more molecules combine to form a single, larger product with no atoms lost as a by-product. Addition reactions occur most commonly at carbon–carbon multiple bonds (alkenes, alkynes) and at polar carbonyl groups, where a reagent adds across the unsaturation. They are fundamental to industrial synthesis — the hydrogenation of vegetable oils, the production of polymers like polyethylene, and the manufacture of alcohols from alkenes all proceed via addition reactions.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental class of organic reactions in which an electron-rich species (nucleophile) attacks a carbon atom bearing a leaving group, displacing that leaving group and forming a new bond. There are two main mechanistic pathways: SN2 (concerted, bimolecular, inverts stereochemistry) and SN1 (stepwise via a carbocation intermediate, gives racemic mixture). These reactions are central to the synthesis of alcohols, ethers, amines, and other functional groups from alkyl halides.
From Greek "elektron" (amber, used historically to describe electricity) + "philos" (loving). The term was introduced by Christopher Ingold in 1933 as the complement to "nucleophile", to describe species that seek electron-rich (nucleophilic) centres in organic molecules.