Muhammad B.

Pericyclic Reactions (Peri mean around and cyclic mean circle) So, Pericyclic mean around the circle. It may be define as: “A pericyclic reaction is a concerted reaction that proceeds through a cyclic transition state.” Characteristics of pericyclic all reactions: 1) All pericyclic reactions are single step mechanism. 2) All pericyclic reactions have conjugated cyclic transition state. 3) All pericyclic reactions are internally self-sufficient mean (no extra reagent and catalyst is required) they initiated by thermally or photo chemically. 4) All pericyclic reactions are stereospecific in nature mean (specific stereoisomer in reactants form specific stereoisomer in products). 5) All pericyclic reactions show equilibrium state mean (reactants and products have ability to inter change with each other). Types of pericyclic reactions: There are following types of pericyclic reactions 1) Electrocyclic reactions 2) Cycloaddition reactions 3) Sigmatropic rearrangement 1) Electrocyclic Reactions “An electrocyclic reaction is a reversible reaction that can involve ring closure or ring opening of one molecule of reactant to form one molecule of product.” Type of Electrocyclic Reactions: i) Electrocyclic ring closure reactions: “An electrocyclic ring closure is an intramolecular reaction that forms a cyclic product containing one more σ bond and one fewer π bond than the reactants.” ii) Electrocyclic ring opening reactions: “An electrocyclic ring opening is a reaction in which an σ bond of a cyclic reactant is cleaved to form a conjugated product with one more π bond.” To draw the product in each reaction, use curved arrows and begin at a π bond. Move the π electrons to an adjacent carbon-carbon bond and continue in a cyclic fashion.