biology

Hexafluorobenzene

Hexafluorobenzene is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hexafluorobenzene rather than just read about it. In short: Hexafluorobenzene, HFB or perfluorobenzene is an organofluorine compound with the chemical formula C6F6. In this derivative of benzene, all hydrogen atoms have been replaced by fluorine atoms.

Key takeaways

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

Reference excerpt

Hexafluorobenzene, HFB or perfluorobenzene is an organofluorine compound with the chemical formula C6F6. In this derivative of benzene, all hydrogen atoms have been replaced by fluorine atoms. The technical uses of the compound are limited, although it has some specialized uses in the laboratory owing to distinctive spectroscopic properties.

Geometry of the aromatic ring Hexafluorobenzene stands somewhat aside in the perhalogenbenzenes. If a perhalogenated benzene ring were to remain planar, then geometric constraints would force adjacent halogens closer than their associated nonbonding radius. Consequently the benzene ring buckles, reducing p-orbital overlap and aromaticity to avoid the steric clash. Perfluorobenzene is an exception: as shown in the following table, two fluorines are small enough to avoid collision, retaining planarity and full aromaticity.

Synthesis The direct synthesis of hexafluorobenzene from benzene and fluorine has not been useful. Instead it is prepared via the Finkelstein reaction of perchlorobenzene and potassium fluoride:

C6Cl6 + 6 KF → C6F6 + 6 KCl Antimony fluoride instead adds to the ring, breaking aromaticity. In principle, various halofluoromethanes pyrolyze to hexafluorobenzene, but commercialization was still in the initial stages in 2000.

Reactions Hexafluorobenzene easily undergoes nucleophilic aromatic substitution. One example is its reaction with sodium hydrosulfide to afford pentafluorothiophenol:

C6F6 + NaSH → C6F5SH + NaF The further reaction of pentafluorophenyl derivatives has long been puzzling, because the non-fluorine substituent has no effect. The second new substituent is always directed para, to form a 1,4-disubstituted-2,3,5,6-tetrafluorobenzene. Hexafluorobenzene is thus a comonomer in certain heavily fluorinated heat-resistant polyethers' synthesis. UV light causes gaseous HFB to isomerize to hexafluoro derivative of Dewar benzene.

Laboratory applications Hexafluorobenzene has been used as a reporter molecule to investigate tissue oxygenation in vivo. It is exceedingly hydrophobic, but exhibits high gas solubility with ideal liquid gas interactions. Since molecular oxygen is paramagnetic it causes 19F NMR spin lattice relaxation (R1): specifically a linear dependence R1= a + bpO2 has been reported. HFB essentially acts as molecular amplifier, since the solubility of oxygen is greater than in water, but thermodynamics require that the pO2 in the HFB rapidly equilibrates with the surrounding medium. HFB has a single narrow 19F NMR signal and the spin lattice relaxation rate is highly sensitive to changes in pO2, yet minimally responsive to temperature. HFB is typically injected directly into a tissue and 19F NMR may be used to measure local oxygenation. It has been extensively applied to examine changes in tumor oxygenation in response to interventions such as breathing hyperoxic gases or as a consequence of vascular disruption. MRI measurements of HFB based on 19F relaxation have been shown to correlate with radiation response of tumors. HFB has been used as a gold standard for investigating other potential prognostic biomarkers of tumor oxygenation such as BOLD (Blood Oxygen Level Dependent), TOLD (Tissue Oxygen Level Dependent) and MOXI (MR oximetry) A 2013 review of applications has been published. HFB has been evaluated as standard in fluorine-19 NMR spectroscopy.

Toxicity Hexafluorobenzene may cause eye and skin irritation, respiratory and digestive tract irritation and can cause central nervous system depression per MSDS. The National Institute for Occupational Safety and Health (NIOSH) lists it in its Registry of Toxic Effects of Chemical Substances as neurotoxicant.

See also Pentafluorobenzene Hexabromobenzene Pentafluoromethylbenzene

References

Further reading Pummer, W. J.; Wall, L. A. (1958). "Reactions of hexafluorobenzene". Science. 127 (3299): 643–644. Bibcode:1958Sci...127..643P. doi:10.1126/science.127.3299.643. PMID 17808882. US patent 3277192, Fielding, H. C., "Preparation of hexafluorobenzene and fluorochlorobenzenes", issued 1966-10-04, assigned to Imperial Chemical Industries Bertolucci, M. D.; Marsh, R. E. (1974). "Lattice parameters of hexafluorobenzene and 1,3,5-trifluorobenzene at −17 °C". Journal of Applied Crystallography. 7 (1): 87–88. Bibcode:1974JApCr...7...87B. doi:10.1107/S0021889874008764. Samojłowicz, C.; Bieniek, M.; Pazio, A.; Makal, A.; Woźniak, K.; Poater, A.; Cavallo, L.; Wójcik, J.; Zdanowski, K.; Grela, K. (2011). "The doping effect of fluorinated aromatic solvents on the rate of ruthenium-catalysed olefin metathesis". Chemistry: A European Journal. 17 (46): 12981–12993. Bibcode:2011ChEuJ..1712981S. doi:10.1002/chem.201100160. PMID 21956694.

Illustrations

Worked examples

Example 1 — a first encounter with Hexafluorobenzene

Start with the simplest possible case. Write down what Hexafluorobenzene claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Hexafluorobenzene 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 Hexafluorobenzene 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 Hexafluorobenzene

In research: Hexafluorobenzene appears in biology 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 Hexafluorobenzene 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: Hexafluorobenzene is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aromatic solvents, Fluorobenzenes, Fluorocarbons, so understanding it makes those chapters shorter.
In everyday life: Look for Hexafluorobenzene 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.

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How to study Hexafluorobenzene in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hexafluorobenzene 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 Hexafluorobenzene out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hexafluorobenzene in simple terms?

Hexafluorobenzene, HFB or perfluorobenzene is an organofluorine compound with the chemical formula C6F6. In this derivative of benzene, all hydrogen atoms have been replaced by fluorine atoms.

Why does Hexafluorobenzene matter?

Because it connects several biology 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 Hexafluorobenzene?

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 Hexafluorobenzene.