Pericyclic reactions are a class of organic reactions that occur through a concerted mechanism, meaning that the bond-making and bond-breaking processes happen simultaneously in a cyclic transition state. These reactions typically involve the rearrangement of electrons in a closed loop, allowing for the formation of new bonds without the need for intermediates. Common types of pericyclic reactions include cycloadditions, sigmatropic rearrangements, and electrocyclic reactions. The driving force behind pericyclic reactions is often the stability of the transition state, which can be influenced by factors such as molecular orbitals and symmetry. These reactions are governed by the Woodward-Hoffmann rules, which help predict the outcome based on the symmetry properties of the involved orbitals. Pericyclic reactions are significant in synthetic organic chemistry due to their efficiency and ability to create complex structures.