A chemical species or reactive group that donates an electron pair to form a new covalent bond. In serine-dependent hydrolysis, an activated oxygen can attack a carbonyl carbon.
An ambident nucleophile can form a bond through more than one atom. An enolate can attack through carbon or oxygen; these give distinct products, although its resonance contributors describe the same ion.
Nucleophilicity describes how readily a species forms a bond by donating an electron pair to a specified electrophile. It is a kinetic property, evaluated by relative reaction rates under stated conditions.
It differs from basicity, which concerns the thermodynamic tendency to accept a proton. A bulky base can be effective at removing a proton while reacting slowly at a crowded carbon center. Solvent, charge, polarizability, and steric effects all influence nucleophilicity, so there is no universal ranking valid for every electrophile and medium.
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A nucleophile is a chemical species that donates an electron pair to form a chemical bond in a reaction. The term "nucleophile" is derived from "nucleus-loving," as nucleophiles are attracted to positively charged or electron-deficient regions in other molecules, often referred to as electrophiles. Nucleophiles are characterized by their electron-rich nature, which allows them to participate in nucleophilic attacks.