Bullvalene

Key takeaways

Bullvalene belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Bullvalene to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Bullvalene from memory before moving on to harder problems.

Reference excerpt

Bullvalene is a hydrocarbon with the chemical formula C10H10. The molecule has a cage-like structure formed by the fusion of one cyclopropane and three cyclohepta-1,4-diene rings. Bullvalene is unusual as an organic molecule due to the C−C and C=C bonds forming and breaking rapidly through Cope rearrangements; this property makes it a fluxional molecule.

Stereodynamics The bullvalene molecule is a cyclopropane platform with three vinylene arms conjoined at a methine group. This arrangement enables a degenerate Cope rearrangement with the result that all carbon atoms and hydrogen atoms appear equivalent on the NMR timescale. At room temperature the 1H NMR signals average to a rounded peak at 5.76 ppm. At lower temperatures the peak broadens into a mound-like appearance, and at very low temperatures the fluxional behavior of bullvalene is reduced, allowing for 4 total signals to be seen. This pattern is consistent with an exchange process whose rate k is close to the frequency separation of the four contributing resonances. The number of possible valence tautomers of a bullvalene depends on the number of unique substituents. The number of isomers with ten distinguishable substituents is 10!/3 = 1,209,600.

Synthesis In 1963, G. Schröder produced bullvalene by photolysis of a dimer of cyclooctatetraene. The reaction proceeds with expulsion of benzene. In 1966 W. von Eggers Doering and Joel W. Rosenthal synthesized it by the photochemical rearrangement of cis-9,10-dihydronaphthalene.

Related compounds

Bullvalones In bullvalones one vinyl group in one of the arms in bullvalene is replaced by a keto group on a methylene bridge. 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 in methanol) 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 in isopentane with acetone as a photosensitizer 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 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 with N-deuteriocyclohexylamide. Photolysis of 2 results in the initial formation of a biradical intermediate with a cyclopropane ring formed. This product rearranges to a second intermediate with a more favorable allylic radical as two mesomers. Intersystem crossing 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. As noted, the conversion of barrelene to semibullvalene is a di-π-methane rearrangement.

A synthetic procedure for alkylated semibullvalenes published in 2006 is based on cyclodimerisation of a substituted 1,4-dilithio-1,3-butadiene with copper(I) bromide. At 140 °C the ethylated semibullvalene isomerises to the cyclooctatetraene derivative.

Barbaralane In barbaralane, one ethylene arm is replaced by a methylene bridge and the dynamics are comparable to that of semibullvalene. There is also an intermediate ketone in bullvalene synthesis called "barbaralone". Both are named after Barbara M. Ferrier, (1932–2006) professor of the Department of Biochemistry and Biomedical Sciences at McMaster University.

Origin of the name The name bullvalene is derived from the nickname of one of the scientists who predicted its properties in 1963 and the underlying concept of valence tautomerism, William "Bull" Doering. According to Klärner in 2011, the weekly seminars organised by Doering were secretly called "Bull sessions" by PhD students and postdocs and "were feared by those who were poorly prepared". The name was bestowed on the molecule, in 1961, by two of Doering's Yale graduate students, Maitland Jones Jr and Ron Magid. The name celebrates Bill Doering's well-known nickname and was chosen to rhyme with fulvalene, a molecule of great interest to the research group.

References

Illustrations

Worked examples

Example 1 — a first encounter with Bullvalene

Start with the simplest possible case. Write down what Bullvalene claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Bullvalene before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Bullvalene ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Bullvalene

In research: Bullvalene appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Bullvalene in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Bullvalene is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cyclopropanes, Dienes, Hydrocarbons, so understanding it makes those chapters shorter.
In everyday life: Look for Bullvalene outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Bullvalene in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Bullvalene means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Bullvalene out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Bullvalene in simple terms?

Bullvalene is a hydrocarbon with the chemical formula C10H10. The molecule has a cage-like structure formed by the fusion of one cyclopropane and three cyclohepta-1,4-diene rings.

Why does Bullvalene matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Bullvalene?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Bullvalene.