Nukleofilit

Nukleofilit, or nucleophilicity, is the property of a chemical species to donate an electron pair to an electrophile, enabling the formation of a new covalent bond. Nucleophiles are typically Lewis bases with regions of high electron density, such as lone pairs or π bonds, and can be anions or neutral molecules.

Nucleophiles participate in a variety of reactions, most notably substitution and addition processes. In SN2 reactions, a nucleophile attacks an electrophilic carbon from the opposite side, leading to a concerted bond formation and often inversion of stereochemistry. Nucleophiles also add to carbonyl groups or activated alkenes, and can engage in rearrangements or polymerization depending on the system. The strength of a nucleophile depends on the substrate and the reaction conditions; for example, hydroxide, alkoxide, cyanide, thiolate, and halide ions are common nucleophiles in organic synthesis.

Several factors influence nucleophilicity. Charge enhances nucleophilicity, but basicity alone does not determine it. Solvent effects are crucial: polar protic solvents solvate small anions strongly, reducing their nucleophilicity, while polar aprotic solvents leave nucleophiles less solvated and more reactive. Steric hindrance can impede attack. Hard and soft nucleophiles, described by HSAB theory, prefer matching electrophile centers; hard nucleophiles (e.g., OH−, F−) favor hard centers, while soft nucleophiles (e.g., I−, RS−) favor soft centers.

Nucleophilicity is distinct from basicity and is context-dependent. A species can be a strong nucleophile yet a weak base, depending on the solvent and substrate.