Bullvalene

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Bullvalene

Bullvalene is a hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon or hydrogen are referred to as "pure" hydrocarbons, whereas other hydrocarbons with bonded com...
with the chemical formula

Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
C₁₀H₁₀ with the unusual property that the chemical bond

Chemical bond

A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds....
s making up the molecule are constantly rearranging as in fluxional molecules. For this reason bullvalene is extensively studied in organic chemistry

Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
. The name bullvalene is derived from the nickname of one the scientists who predicted its properties in 1963, William "Bull" Doering

William von Eggers Doering

William von Eggers Doering is a Professor Emeritus at Harvard University and the former Chair of its Chemistry Department.He is known in the field of organic chemistry for his work on quinine....
and the underlying concept of valence tautomerism.

bullvalene molecule is a cyclopropane

Cyclopropane

Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms....
platform with three vinyl

Vinyl

A vinyl compound is any organic compound that contains a vinyl group , −CarbonHydrogenCovalent bondCH2. These are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group....
arms connecting with a methine

Methine

In chemistry, methyne is a tri-valent functional group CH, derived formally from methane. The methine group consists of a carbon atom bound by two single covalent bonds and one double bond, where one of the single bonds is to a hydrogen....
group.

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Encyclopedia

Bullvalene is a hydrocarbon

Hydrocarbon

Chemical formula

Chemical bond

Organic chemistry

William von Eggers Doering

Bullvalene

The bullvalene molecule is a cyclopropane

Cyclopropane

Vinyl

Methine

Cope rearrangement

The Cope rearrangement is an extensively studied organic reaction involving the sigmatropic rearrangement of 1,5-dienes . It was developed by Arthur C....
s with the result that all carbon atoms and hydrogen atoms are equivalent and that none of the carbon-carbon bonds is permanent. The number of possible valence tautomers is 10!

Factorial

In mathematics, the factorial of a negative and non-negative numbers integer n, denoted by n!, is the Product of all positive integers less than or equal to n....
/3 = 1,209,600. The rearrangements displayed in scheme 1 are only 5 of them.

The compound was first synthesised in 1963 by G. Schröder by photolysis of a dimer of cyclooctatetraene

Cyclooctatetraene

1,3,5,7-Cyclooctatetraene is an saturation derivative of cyclooctane, with the formula C8H8. It is also known as [8]annulene....
with expulsion of benzene

Benzene

Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
.

The unusual dynamic properties of bullvalene show up in proton NMR

Proton NMR

Proton NMR is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 Atomic nucleus within the molecules of a substance, in order to determine the structure of its molecules....
. In a spectrum taken at room temperature a broad peak is visible representing many different protons. The spectrum at 120 °C on the other hand shows just one peak at 4.2 ppm. At this temperature the bullvalane protons are rearranging faster than the NMR can resolve resonances, this is largely due to the Heisenberg Uncertainty Principle (energy/time formulation).

Bullvalones

In bullvalones one vinyl group in one of the arms in bullvalene is replaced by a ketone

Ketone

In organic chemistry, a ketone is a type of organic compound which contains a carbonyl group bonded to two other carbon atoms in the form:Neither of the substituents R1 and R2 may be equal to hydrogen ....
group. In this way it is possible to activate the fluxional state by adding base and deactivate it again by removing the base:

Compound 1 in scheme 2 is not a fluxional molecule but by adding base (sodium methoxide

Sodium methoxide

Sodium methoxide is a Compound , with formula NaOCH3. This colourless solid, which is formed by the deprotonation of methanol, is a widely used reagent in industry and the laboratory....
in methanol

Methanol

Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a chemical compound with chemical formula carbonhydrogen3oxygenhydrogen ....
) the ketone converts to the enolate 2 and the fluxional state is switched on. Deuterium labeling is possible forming first 3 a then a complex mixture with up to 7 deuterium atoms, compound 4 being just one of them.

Semibullvalene

In semibullvalene (C₈H₈), one ethylene arm is replaced by a single bond. The compound was first prepared by photolysis of barrelene

Barrelene

Barrelene is a bicyclic organic compound with chemical formula C8H8 and systematic name bicyclo[2.2.2]octa-2,5,7-triene. First synthesized and described by H....
in toluene

Toluene

Toluene, also known as methylbenzene or phenylmethane, is a clear, Water -insoluble liquid with the typical smell of paint thinners, redolent of the sweet smell of the related compound benzene....
with acetone

Acetone

Acetone is the organic compound with the chemical formula OC2. This colorless, mobile, flammable liquid is the simplest example of the ketones....
as a photosensitizer

Photosensitizer

In pharmacology, a photosensitizer is a drug, food, or other chemical that increases photosensitivity of the organism. This may be an adverse effect of many drugs, or a desired effect in photodynamic therapy of tumors....
in 1966.

Semibullvalene exists only as two valence tautomers (2a and 2b in scheme 3) but in this molecule the Cope rearrangement takes place even at -110 °C, a temperature at which this type of reaction is ordinarily not possible.

One insight into the reaction mechanism

Reaction mechanism

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs .Although only the net chemical change is directly observation for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in a reaction mechanism....
for this photoreaction is given by an isotope scrambling experiment. The 6 vinylic protons in barrelene 1 are more acidic than the two bridgehead protons and therefore they can be replaced by deuterium

Deuterium

Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen ....
with N-deuteriocyclohexylamide. Photolysis of 2 results in the initial formation of an biradical intermediate with a cyclopropane ring formed. This product rearranges to a second intermediate with a more favorable allyl

Allyl

An allyl group is an alkene hydrocarbon group with the formula H2C=CH-CH2-. It is made up of a vinyl group, CH2=CH-, attached to a methylene -CH2....
ic radical as two mesomers. Intersystem crossing

Intersystem crossing

Intersystem crossing is a photophysical process. An isoenergetic non-radiative transition between two electronic states having different Term symbol....
and radical recombination results in equal quantities of semibullvalenes 3 and 4. The new proton distribution with allylic, vinylic and cyclopropanyl protons determined with proton NMR confirms this model.

A new synthetic procedure for alkylated semibullvalenes published in 2006 is based on cyclodimerization of a 1,4-dilithio-1,3-diene with copper(I) bromide

Copper(I) bromide

Copper bromide is the chemical compound with the chemical formula CuBr. This diamagnetic solid adopts a polymeric structure akin to that for zinc sulfide....
. At 140 °C the ethylated semibullvalene isomerises to the cyclooctatetraene

Cyclooctatetraene

1,3,5,7-Cyclooctatetraene is an saturation derivative of cyclooctane, with the formula C8H8. It is also known as [8]annulene....
derivative.

Barbaralane

In barbaralane one ethylene arm is replaced by a methylene

Methylene

Methylene is the chemical species, R2C:, named after methane, in which two of the carbon atom's valence electrons form no bonds. The word is applicable to:...
group and the dynamics are comparable to that of semibullvalene.