nucleofiili

Nucleofiili are chemical species that donate an electron pair to an electrophile, enabling the formation of a new chemical bond. They are central to many reactions in organic synthesis, including nucleophilic substitutions and nucleophilic additions to carbonyl compounds. Nucleofiili can be anions such as CN-, OH-, RO-, and RS-, or neutral species such as ammonia, amines, water, alcohols, and many organometallic reagents. Although many nucleofiili also act as bases, nucleophilicity and basicity are not identical; a strong base is not necessarily a strong nucleophile in a given solvent, and nucleophilicity depends on the reaction environment and the electrophile involved.

Several factors govern nucleophilicity. Electron-rich, negatively charged species are typically good nucleofiili, but steric hindrance can hinder their approach to the electrophile. Polarizability also matters: soft nucleofiili such as I-, RS- are highly nucleophilic toward soft electrophiles, whereas hard nucleofiili like F- are less reactive toward carbon centers in protic solvents. Solvent effects are important: in polar protic solvents, nucleophilicity often increases down a group (I- > Br- > Cl- > F-), while in polar aprotic solvents the order tracks basicity (F- > Cl- > Br- > I-). Temperature, solvent polarity, and the presence of metal centers (as in Grignard reagents or organolithiums) can modify reactivity.

Nucleofiili are exploited in many bond-forming steps such as SN2 reactions, additions to aldehydes and ketones, and nucleophilic substitutions on alkyl halides. They are classified within the broader framework of nucleophilicity, a property related to, but distinct from, basicity, and they are analyzed using concepts such as HSAB theory and relative rate measurements.