Nucleophile
An electron-rich species that donates a pair of electrons to form a new covalent bond.
Formula / equation
Nu⁻ or Nu:
Unit
Dimensionless
In depth
Nucleophiles are Lewis bases and are attracted to electron-poor centres. Their strength depends on charge, on the electronegativity and polarisability of the donor atom, and on the solvent, which is why iodide outperforms fluoride in protic solvents despite being less basic.
Examples in the real world
OH⁻, CN⁻, NH₃, water and halide ions; the hydride ion delivered by borohydride reagents.