In organic chemistry

Organic chemistry

Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...

, a pericyclic reaction is a type of organic reaction

Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis,...

 wherein the transition state

Transition state

The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always...

 of the molecule has a cyclic geometry, and the reaction progresses in a concerted

Concerted reaction

In chemistry, a concerted reaction is a chemical reaction in which all bond breaking and bond making occurs in a single step. Reactive intermediates or other unstable high energy intermediates are not involved. Concerted reaction rates tend not to depend on solvent polarity ruling out large buildup...

 fashion. Pericyclic reactions are usually rearrangement reaction

Rearrangement reaction

A rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another atom in the same molecule...

s. The major classes of pericyclic reactions are:

Name	Bond changes
	Sigma	Pi
Electrocyclic reaction Electrocyclic reaction In organic chemistry, an electrocyclic reaction is a type of pericyclic rearrangement reaction where the net result is one pi bond being converted into one sigma bond or vice-versa...	+ 1	-1
Cycloaddition Cycloaddition A cycloaddition is a pericyclic chemical reaction, in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a cyclization reaction.Cycloadditions are usually described by the...	+2	-2
Sigmatropic reaction Sigmatropic reaction A sigmatropic reaction in organic chemistry is a pericyclic reaction wherein the net result is one σ-bond is changed to another σ-bond in an uncatalyzed intramolecular process. The name sigmatropic is the result of a compounding of the long-established sigma designation from single carbon-carbon...	0	0
Group transfer reaction Group transfer reaction Group transfer reactions are pericyclic reactions where one pi bond is converted to one sigma bond, at the same time that a sigma bond migrates.The best known group transfer reaction is the ene reaction....	+ 1	-1
Cheletropic reaction Cheletropic reaction thumb|300px|right|Pericyclic ReactionsCheletropic reactions are a type of pericyclic reaction. A pericyclic reaction is one that involves a transition state with a cyclic array of atoms and an associated cyclic array of interacting orbitals. A reorganization of σ and π bonds occurs in this cyclic...	+ 2	- 2
Dyotropic reaction Dyotropic reaction A dyotropic Reaction in organic chemistry is a type of organic reaction and more specifically a pericyclic valence isomerization in which two sigma bonds simultaneously migrate intramolecularly...	0	0

In general, these are considered to be equilibrium processes

Chemical equilibrium

In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

, although it is possible to push the reaction in one direction by designing a reaction by which the product is at a significantly lower energy level; this is due to a unimolecular interpretation of Le Chatelier's principle

Le Châtelier's principle

In chemistry, Le Chatelier's principle, also called the Chatelier's principle, can be used to predict the effect of a change in conditions on a chemical equilibrium. The principle is named after Henry Louis Le Chatelier and sometimes Karl Ferdinand Braun who discovered it independently...

.
Pericyclic reactions often have related stepwise radical

Radical (chemistry)

Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 processes associated with them. Some pericyclic reactions, such as the [2+2] cycloaddition, are 'controversial' because their mechanism is not definitively known to be concerted (or may depend on the reactive system). Pericyclic reactions also often have metal-catalyzed analogs, although usually these are also not technically pericyclic, since they proceed via metal-stabilized intermediates, and therefore are not concerted.

A large photoinduced hydrogen sigmatropic shift was utilized in a corrin

Corrin

Corrin is an heterocyclic compound. It is the parent macrocycle related to substituted derivative that is found in vitamin B12. Its name reflects that it is the "core" of vitamin B12 .-Coordination chemistry:...

 synthesis performed by Albert Eschenmoser

Albert Eschenmoser

Albert Eschenmoser is a Swiss chemist working at the ETH Zurich and The Scripps Research Institute.His work together with Lavoslav Ružička on terpenes and the postulation of squalene cyclization to form lanosterol improved the insight into steroid biosynthesis.In the early 1960s, Eschenmoser began...

 containing a 16π system.

Due to the principle of microscopic reversibility

Microscopic reversibility

The principle of Microscopic reversibility in physics and chemistry is twofold:* First, it states that the microscopic detailed dynamics of particles and fields is time-reversible because the microscopic equations of motion are symmetric with respect to inversion in time ;* Second, it relates to...

, there is a parallel set of "retro" pericyclic reactions, which perform the reverse reaction.

Pericyclic reactions in biochemistry

Pericyclic reactions also occur in several biological processes.

• Claisen rearrangement
  Claisen rearrangement
  The Claisen rearrangement is a powerful carbon-carbon bond-forming chemical reaction discovered by Rainer Ludwig Claisen...
  
   of chorismate to prephenate in almost all prototrophic organisms.
• [1,5]-sigmatropic shift in the transformation of precorrin-8x
  Corrin
  Corrin is an heterocyclic compound. It is the parent macrocycle related to substituted derivative that is found in vitamin B12. Its name reflects that it is the "core" of vitamin B12 .-Coordination chemistry:...
  
   to hydrogenobyrinic acid
• non-enzymatic, photochemical electrocyclic ring opening and a (1,7) sigmatropic hydride shift in vitamin D
  Vitamin D
  Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
  
   synthesis.
• a conversion of Isochorismate into salicylate and Pyruvate in a catalyzed, true pericyclic reaction .