| Lewis Base | Nucleophile | Lowry Bronsted Base |
---|---|---|---|
Nature | Donates Electron Pair to any electron-deficient center. Nucleophiles and Lowry Bronsted bases are Lewis bases. | Donates Electron Pair, mostly forming bonds with carbon. The term is commonly used to describe organic chemistry reactions. | Donates electron pair to only H+, therefore, only accepts H+. |
Requirement | Base requires at least one electron pair. | All nucleophiles are Lewis bases. Three types- lone pair containing (neutral and charged), pie bond, and sigma bond donors commonly form bonds with carbon. | Base requires at least one electron pair. |
Bond | May form reversible co-ordinate covalent bond that forms and breaks at room temperature. Strong bases undergo complete reaction. | Forms an irreversible covalent bond that is fixed in the final product. | Weak bases form reversible co-ordinate covalent bond that forms and breaks at room temperature. Strong bases undergo complete reaction. |
Representation | |||
Under equilibrium conditions | After the Lewis base donates an electron pair, conjugate acid is formed. | A charged intermediate formation is seen in multi-step reactions wherein the first step may be reversible. | After the Lowry Bronsted base accepts H+, conjugate acid is formed. |
Steric | Lewis base is an electron donor to any electron-deficient counterpart, including the smallest-sized H+. Therefore, steric preference is not required. | New bond formation requires electron-rich centers capable of donation to be sterically uncrowded. | Lowry-Bronsted base is an acceptor of the smallest proton, H+. Therefore, steric preference is not required. |
Type of reactions | Forms Lewis Acid-Base type of complexes or adducts in equilibrium reactions. In addition, Lewis bases are seen in proton transfer reactions, neutralization reactions, ionization reactions, and addition and substitution reactions. | If a reversible reaction forms an intermediate, the final product is stable, having a new covalent bond. Most nucleophile reactions are addition or substitution reactions. | Lowry Bronsted bases are seen in proton transfer reactions, neutralization reactions involving acids and bases to form salts, and aqueous ionization reactions.
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Role of pKa, Stability and Examples | Neutral or negatively charged electron pair donors. The least stable, highly electronegative and reactive negatively charged species are strong Lewis bases. Strong bases are identified using pKa values. Acids with high pKa give strong Lewis bases that mainly donate to H+. Examples- H−, CN−, CH3COO−, :NH3, H2O, H-, F- | Nucleophiles are less electronegative and more electropositive with pKa values lower than proton abstracting Lewis bases. Sometimes, a strong base by proton abstraction may generate a good nucleophile. Examples- OH−, CN−, :NH3, H2O, I-, Cl-, Br-, C6H6, AlH4- | The least stable, highly electronegative and reactive negatively charged species with the highest pKa are strong Lowry-Bronsted bases. For example, NH2-, CH3-, -OH etc. Other slightly stable Lowry-Bronsted bases are CO32-, HSO3-, HPO42-, Cl-, etc. |
Constant | Equilibrium reactions are thermodynamically controlled and dependent on equilibrium constants. | Reactions involving nucleophiles and new bond formation are kinetically controlled and involve rate constants. | Equilibrium reactions are thermodynamically controlled and dependent on equilibrium constants. |
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