Cope rearrangement

The Cope rearrangement is an extensively studied 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 and redox reactions. In organic synthesis, organic reactions are used...

 involving the [3,3]-sigmatropic rearrangement of 1,5-dienes . It was developed by Arthur C. Cope

Arthur C. Cope

Arthur C. Cope was a highly successful and influential organic chemist and member of the National Academy of Sciences. He is credited with the development of several important chemical reactions which bear his name including the Cope elimination and the Cope rearrangement.Cope was born on June...

. For example 3-methyl-1,5-hexadiene heated to 300°C yields 1,5-heptadiene.

The Cope rearrangement causes the fluxional states of the molecules in the bullvalene

Bullvalene

Bullvalene is a hydrocarbon with the chemical formula C₁₀H₁₀ with the unusual property that the chemical bonds making up the molecule are constantly rearranging as in fluxional molecules. For this reason bullvalene is extensively studied in organic chemistry...

 family.

Although the Cope rearrangement is 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...

 and pericyclic, it can also be considered to go via a 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...

 that is energetically and structurally equivalent to a diradical

Radical (chemistry)

In chemistry, radicals are atoms, molecules, or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions...

.

The Cope rearrangement is an extensively studied 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 and redox reactions. In organic synthesis, organic reactions are used...

 involving the [3,3]-sigmatropic rearrangement of 1,5-dienes . It was developed by Arthur C. Cope

Arthur C. Cope

Arthur C. Cope was a highly successful and influential organic chemist and member of the National Academy of Sciences. He is credited with the development of several important chemical reactions which bear his name including the Cope elimination and the Cope rearrangement.Cope was born on June...

. For example 3-methyl-1,5-hexadiene heated to 300°C yields 1,5-heptadiene.

The Cope rearrangement causes the fluxional states of the molecules in the bullvalene

Bullvalene

Bullvalene is a hydrocarbon with the chemical formula C₁₀H₁₀ with the unusual property that the chemical bonds making up the molecule are constantly rearranging as in fluxional molecules. For this reason bullvalene is extensively studied in organic chemistry...

 family.

Mechanism

Although the Cope rearrangement is 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...

 and pericyclic, it can also be considered to go via a 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...

 that is energetically and structurally equivalent to a diradical

Radical (chemistry)

In chemistry, radicals are atoms, molecules, or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions...

. This is an alternative explanation which remains faithful to the uncharged nature of the Cope transition state, while preserving the principles of orbital symmetry. This also explains the high energy requirement to perform a Cope rearrangement. Although illustrated in the chair conformation, the Cope can also occur with cyclohexadienes in the "boat" conformation.

Examples

The rearrangement is widely used in organic synthesis. It is symmetry

Symmetry

Symmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection...

-allowed when it is suprafacial on all components. The transition state of the molecule passes through a boat or chair like transition state. An example of the Cope rearrangement is the expansion a cyclobutane

Cyclobutane

Cyclobutane is an organic compound with the formula ₄. Cyclobutane is a colourless gas and commercially available as a liquefied gas. Derivatives of cyclobutane are called cyclobutanes...

 ring to a 1,5-cyclooctadiene

1,5-Cyclooctadiene

1,5-Cyclooctadiene is the organic compound with the chemical formula C₈H₁₂. Generally abbreviated COD, this diene is a useful precursor to other organic compounds and serves as a ligand in organometallic chemistry.-Synthesis:...

 ring:



In this case, the reaction must pass through the boat 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...

 to produce the two cis

Geometric isomerism

In organic chemistry, cis-trans isomerism or geometric isomerism or configuration isomerism or E-Z isomerism is a form of stereoisomerism describing the orientation of functional groups within a molecule. In general, such isomers contain double bonds, which cannot rotate, but they can also arise...

 double bond

Double bond

A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...

s. A trans double bond in the ring would be too strained

Ring strain

Ring strain is an organic chemistry term that describes the destabilization of a cyclic molecule—such as a cycloalkane—due to the non-favorable high energy spatial orientations of its atoms...

. The reaction occurs under thermal conditions. The driving force of the reaction is the loss of strain from the cyclobutane ring.

Oxy-Cope rearrangement

In the Oxy-Cope rearrangement a hydroxyl

Hydroxyl

In chemistry, hydroxyl is composed of molecules consisting of an oxygen atom and a hydrogen atom connected by a covalent bond . The neutral form is a hydroxyl radical. The hydroxyl anion is called hydroxide; it is a diatomic ion with a charge of negative one...

 group is added at C3 forming a enal or enone after Keto-enol tautomerism

Keto-enol tautomerism

In organic chemistry, keto-enol tautomerism refers to a chemical equilibrium between a keto form and an enol. The enol and keto forms are said to be tautomers of each other...

 of the intermediate enol :

for instance in this reaction:

Variations

Another variation of the Cope rearrangement is the heteroatom Cope reactions such as the Aza-Cope rearrangement. Another widely studied [3, 3] sigmatropic rearrangement is the Claisen rearrangement

Claisen rearrangement

The Claisen rearrangement is a powerful carbon-carbon bond-forming chemical reaction discovered by Rainer Ludwig Claisen. The heating of an allyl vinyl ether will initiate a [3,3]-sigmatropic rearrangement to give a γ,δ-unsaturated carbonyl....

.