In catalytic cycles, protonation and deprotonation often act as key steps that govern the mechanism of the reaction. For instance, in the case of the Friedel-Crafts alkylation, the protonation of the catalyst (usually a Lewis acid like AlCl₃) activates the electrophile, facilitating its attack on the aromatic ring. Similarly, in enzyme catalysis, protonation states of amino acid residues in the active site can be crucial for substrate binding and transformation.
