In organic chemistry, how is a "nucleophile" defined?

A nucleophile is defined as a species that donates an electron pair to form a bond. This donation is essential in chemical reactions, especially in nucleophilic substitution and addition reactions where the nucleophile attacks an electrophile, which is a species that accepts the electron pair. The ability of a nucleophile to donate electrons is crucial for driving the reaction forward, as it often leads to the formation of new covalent bonds. Common examples of nucleophiles include anions such as hydroxide (OH⁻) or halides (Cl⁻, Br⁻), as well as neutral molecules with lone pairs, such as ammonia (NH₃) or water (H₂O). Their reactivity stems from their electron-rich nature, making them more likely to seek out positively charged or electron-deficient species.