nucleofiele

A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond. Nucleophiles are Lewis bases by definition and are drawn to positively polarized centers. They commonly attack electrophilic carbon atoms in alkyl halides and carbonyl carbons in aldehydes and ketones, but they can also engage electrophilic atoms such as sulfur, phosphorus, or metal centers in coordination reactions.

Nucleophiles can be negatively charged or neutral. Their reactivity is influenced by charge, sterics, and solvent. Hard nucleophiles (for example, hydroxide and alkoxides) tend to attack hard electrophiles, while soft nucleophiles (such as iodide, thiolates, and phosphides) prefer soft electrophiles. Ambident nucleophiles, like cyanide or thiocyanate, can attack through different atoms. Solvent effects are important: in protic solvents, nucleophilicity often increases down a group (I− > Br− > Cl− > F−); in polar aprotic solvents, nucleophilicity often follows basicity (F− > Cl− > Br− > I−).

Mechanistically, nucleophiles participate in substitution or addition reactions. In SN2 processes, nucleophilicity is a primary determinant of the reaction rate and is hindered by steric bulk. In SN1 processes, nucleophile strength has a smaller effect on the rate, though it influences the final product distribution and capture of the carbocation. Nucleophilicity and basicity are related but distinct; a species can be a strong base yet a weak nucleophile in a given solvent.

Nucleophiles are central to organic synthesis, polymerization, and many biological transformations, where nucleophilic attack on electrophilic centers shapes the formation of new bonds and molecular frameworks.