Elektrofiilis

Elektrofiilis (electrophilicity) is a chemical property describing the tendency of a species to accept electrons, especially from nucleophiles, in a reaction. In theoretical descriptions, electrophilicity can be quantified using the electrophilicity index ω = μ^2/(2η), where μ is the chemical potential and η is the chemical hardness. A larger ω corresponds to a stronger electrophile and a faster reaction with a given nucleophile under similar conditions.

Electrophilicity is influenced by electronic structure: electron-withdrawing groups and electron-deficient centers raise electrophilicity by lowering the energy of the lowest unoccupied molecular orbital and by stabilizing developing negative charge on the nucleophile’s side. Leaving groups and resonance structures that generate positive charge at the reactive center also increase electrophilicity. Solvent and coordination effects matter: polar solvents can stabilize charge separation in the transition state, and Lewis acids can enhance electrophilicity by binding to electron-rich sites and increasing positive character at the reaction center.

Experimentally, electrophilicity is often assessed by reactivity toward standard nucleophiles. The Mayr–Patz electrophilicity scale assigns an electrophilicity parameter E to reagents, which, together with a nucleophile parameter N and a sensitivity factor s, predicts rate constants through a relationship such as log k = s_N (N + E). The concept also relates to HSAB theory: hard electrophiles tend to react with hard nucleophiles, soft with soft.

Examples of electrophiles include carbonyl compounds, acyl halides, carbocations, and activated olefins. The study of elektrofiilis spans theoretical indices, empirical reactivity scales, and practical considerations in synthesis and catalysis.