A Lewis acid-base reaction occurs when a base donates a pair of electrons to an acid. ... A Brønsted-Lowry acid such as HCl is an acid-base adduct according to the Lewis concept, and proton transfer occurs because a more stable acid-base adduct is formed.
Example: Water (H2O) has two nonbonding pairs of electrons, so it donates one pair to the carbocation. As a result, one bond is formed and shared between carbon and oxygen. Water acts as a Lewis base because it is the electron pair donor in this reaction.
