Nukleofiils

Nukleofiils (nucleophiles) are chemical species that donate an electron pair to an electrophile to form a chemical bond. They are typically electron-rich and can carry a negative charge, possess lone pairs, or have π electrons that can be donated to electron-poor centers.

Common nukleofiils include hydroxide (OH−), alkoxides (RO−), cyanide (CN−), thiolates (RS−), amines (R3N), enolates, and halide ions such as Cl− and Br− in suitable contexts. Neutral nukleofiils such as water and ammonia can also participate. The strength of a nukleofiil depends on charge, polarizability, and the solvent.

Most nucleophilic reactions occur in substitution or addition mechanisms. In SN2, a strong nukleofiil attacks the substrate carbon as the leaving group departs. In SN1, nucleophile strength is less important and the rate is determined by carbocation formation. Nukleofiils also attack carbonyl groups in nucleophilic additions, as in the formation of alcohols from aldehydes and ketones with various reagents or in acyl substitutions with amines.

Solvent effects are significant. In polar protic solvents, nucleophilicity often increases with polarizability and down a group (I− > Br− > Cl− > F−), while in polar aprotic solvents the trend follows basicity (F− > Cl− > Br− > I−). Nukleofiils are central to organic synthesis and biological catalysis, enabling bond formation and transformation under a wide range of conditions.