Pre-Requisite Reading: Nucleophiles, Electrophiles
Lewis acids and electrophiles are electron acceptors, and sometimes, the term is used interchangeably. However, all Lewis acids are not electrophiles since forming a covalent bond is an important step in an electrophile–nucleophile reaction.
Most Lewis acid reactions in organic chemistry involve the formation of a complex/adduct using a coordinate covalent bond. The coordinate covalent bond is a weak bond that can repeatedly form and dissociate (reversible) at or near room temperature.
In contrast, reactions with an electrophile form a stable, fixed covalent bond in the final product. Though there is chance that initial reaction steps may be reversible that is necessary to form a reaction intermediate, however, in the final product, the bond of the electrophile with the nucleophile will become fixed.
In the reaction involving carbon electrophiles that have a weak bond (pie bond or bonds to the leaving group) in the molecule, the incoming nucleophile must break these bonds. Only then can a new covalent bond be formed, maintaining the Carbon valency at four. Losing the weak bond to create a stronger covalent bond produces more stable molecules.
For example, the attack of the nucleophile on the carbonyl carbon breaks its pie bond.
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Quiz on Lewis Acids Versus Electrophiles
