Base vs Nucleophile: Key Differences with Examples
In organic chemistry, the terms base and nucleophile are often used, sometimes interchangeably, but they represent different chemical roles. Understanding the distinction is crucial for mastering reaction mechanisms.
What is a Base?
A base is a species that accepts a proton (H⁺) according to the Brønsted-Lowry theory.
Example:
Hydroxide ion (OH⁻) acting as a base:
Here, OH⁻ accepts a proton from acetic acid.
What is a Nucleophile?
A nucleophile is a species that donates a lone pair of electrons to an electrophile (electron-deficient atom) to form a covalent bond.
Example:
Hydroxide ion (OH⁻) acting as a nucleophile:
Here, OH⁻ attacks the carbon in CH₃Br (a partial positive centre), replacing the Br⁻.
Key Differences
| Property | Base | Nucleophile |
|---|---|---|
| Main Function | Accepts H⁺ | Donates a lone pair to form a bond |
| Target | Proton (H⁺) | Electrophilic carbon (δ⁺) |
| Reactivity | In acid-base reactions | In substitution/addition reactions |
| Example | OH⁻ with CH₃COOH | OH⁻ with CH₃Br |
Same Species, Different Roles
Many species can act as both a base and a nucleophile, depending on the reaction.
-
Base role: Focuses on abstracting protons.
-
Nucleophile role: Focuses on attacking electron-deficient centres.