What is Pericyclic reaction?
[[File:Cycloheptatriene-Norcaradiene Rearrangement.png|right|300px|Example of a pericyclic reaction the [[Cyclohexatriene]] [[norcaradiene]] rearrangement]] In [[organic chemistry]], a '''pericyclic reaction''' is a type of [[organic reaction|chemical reaction between organic compounds]]. In the case of pericyclic reactions, the [[transition state]] of the molecule is a ring (has a cyclic geometry), and the reaction goes forward in a [[concerted reaction|concerted]] way. Pericyclic reactions are usually [[rearrangement reaction]]s. The most important groups of pericyclic reactions are: * [[Electrocyclic reaction]]s * [[Cycloaddition]]s * [[Sigmatropic reaction]]s * [[Group transfer reaction]]s * [[Cheletropic reaction]]s * [[Dyotropic reaction]]s In general, pericyclic reactions are [[Chemical equilibrium|equilibrium processes]]. However, it is possible to push the reaction in one direction if the product is at a significantly lower [[energy level]]. This is applying [[Le Chatelier's principle]] to a reaction involving a single [[molecule]]. Many pericyclic reactions have similar stepwise [[Radical (chemistry)|radical]] processes connected with them. Chemists disagree whether some reactions are pericyclic reactions. For example, it is not definitively known whether the [2+2] [[cycloaddition]] mechanism is concerted (or may depend on the reactive system). Many pericyclic reactions have similar reactions that are metal-[[Catalysis|catalyzed]]. But these metal-catalyzed reactions are not really pericyclic. The metal [[catalyst]]s stabilize the reaction intermediates. So the reaction is not concerted, but rather metal-stabilized. A large photoinduced hydrogen [[sigmatropic]] shift was utilized in a [[corrin]] synthesis performed by [[Albert Eschenmoser]] containing a 16π system.<ref>A New Type of Corrin Synthesis. Yasuji Yamada, D. Miljkovic, P. Wehrli, B. Golding, P. Loliger, R. Keese, K. Miiller, and A. Eschenmoser. [http://www3.interscience.wiley.com/cgi-bin/fulltext/106576485/PDFSTART ''Angew. Chem. Int. E