Nukleophiles

Nucleophiles are species that donate an electron pair to an electrophilic center, forming a chemical bond. They are Lewis bases by definition and play a central role in many organic and inorganic reactions. A nucleophile is typically electron-rich, bearing lone pairs or π electrons that can be shared with an electron-poor atom.

Common nucleophiles include anions such as hydroxide (OH−), alkoxides (RO−), cyanide (CN−), amide (NH2−), and halide ions (I−, Br−, Cl−). Neutral nucleophiles such as ammonia (NH3), amines (RNH2, R2NH), water (H2O), and alcohols (ROH) can also act as nucleophiles. Organometallic reagents, for example Grignard reagents (RMgX) and organolithiums, are highly nucleophilic at carbon.

Nucleophiles participate in a variety of mechanisms. In alkyl substitutions, SN2 reactions involve a concerted backside attack at a carbon with displacement of a leaving group. SN1 mechanisms proceed via carbocation intermediates and can lead to rearrangements. Nucleophiles also add to carbonyl groups (nucleophilic additions) and engage in nucleophilic acyl substitutions with acyl chlorides and related derivatives. The HSAB principle explains preference for soft or hard electrophiles.

Several factors influence nucleophilicity, including solvent effects, steric hindrance, charge, and the leaving-group ability of the electrophile. In protic solvents, nucleophilicity generally increases down a group; in polar aprotic solvents, nucleophilicity aligns more closely with basicity. Nucleophiles are fundamental for bond formation in synthesis, catalysis, and material science. See also nucleophile, electrophile, SN1, SN2, and HSAB theory.