Nukleofilis

Nukleofilis, or nucleophilicity, is the tendency of a molecule or ion to donate an electron pair to an electron-poor center (an electrophile) in a chemical reaction, forming a covalent bond. Nucleophiles typically contain lone pairs or π bonds and are drawn to partial positive charges. Nucleophilicity is a kinetic concept that describes reaction rate and is distinct from basicity, which is a measure of proton affinity.

Common nucleophiles include hydroxide, cyanide, alkoxide, amines, thiolates, and halide ions. Nucleophiles initiate or participate in many substitution and addition reactions, such as SN2 on alkyl halides or nucleophilic additions to carbonyl compounds. The strength of nucleophilicity depends on multiple factors beyond charge, including electron density, polarizability, and steric hindrance, as well as solvent and temperature.

Solvent effects are especially important. In protic solvents, nucleophilicity often increases in the order F− < Cl− < Br− < I− due to decreasing solvation of larger ions, leading to stronger nucleophiles for heavier halides. In aprotic solvents, nucleophilicity correlates more closely with basicity, so the trend can reverse. Hard–soft acid–base considerations (HSAB), polarizability, and the nature of the leaving group also influence nucleophilicity.

Nukleofilis is a central concept in organic synthesis and related fields, guiding the choice of reagents and conditions for substitution and addition reactions. It is typically quantified or compared by measuring reaction rates (for example, SN2 rate constants) under specific, defined conditions.