Pericyclic Reactions -What Are They? Pericyclic reaction All bonding changes occur simultaneously through a cyclic transition state The combination of steps is called a concerted process; no intermediates are involved Why this chapter? Understanding of pericyclic reactions emerged in the latter half of the twentieth century Some biological pathways proceed through pericyclic reactionsPericyclic reaction • All bonding changes occur simultaneously through a cyclic transition state • The combination of steps is called a concerted process; no intermediates are involved Why this chapter? • Understanding of pericyclic reactions emerged in the latter half of the twentieth century • Some biological pathways proceed through pericyclic reactions Pericyclic Reactions – What Are They?