A pericyclic reaction is a type of organic reaction that involves the concerted rearrangement of electrons in a cyclic manner. These reactions typically occur in a single step without intermediates, allowing for the formation of new bonds while breaking existing ones. Common examples include Diels-Alder reactions and electrocyclic reactions, which are important in synthetic organic chemistry. Pericyclic reactions are governed by the principles of molecular orbital theory and are often classified based on their mechanisms, such as cycloadditions, sigmatropic rearrangements, and group transfer reactions. They are characterized by their stereospecificity and regioselectivity, making them valuable for constructing complex molecular architectures.