chemistry

Hexamethyl Dewar benzene

Hexamethyl Dewar benzene is a chemistry 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 Hexamethyl Dewar benzene rather than just read about it. In short: Hexamethyl Dewar benzene is a derivative of Dewar benzene with application in organometallic chemistry. It consists of the Dewar benzene core, with a methyl group substituent on each of its six carbon positions.

Key takeaways

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

Reference excerpt

Hexamethyl Dewar benzene is a derivative of Dewar benzene with application in organometallic chemistry. It consists of the Dewar benzene core, with a methyl group substituent on each of its six carbon positions.

Synthesis Hexamethyl Dewar benzene has been prepared by bicyclotrimerization of dimethylacetylene with aluminium chloride.

Rearrangement to cyclopentadienes Hexamethyl Dewar benzene undergoes a rearrangement reaction with hydrohalic acids to give a cyclopentadiene structure. A rhodium or iridium salt in methanol can be added to it to form the organometallic pentamethylcyclopentadienyl rhodium dichloride and pentamethylcyclopentadienyl iridium dichloride dimers; Consequently, it can be used as a starting material for synthesising some pentamethylcyclopentadienyl organometallic compounds including [Cp*Rh(CO)2]. The hydrogen halide reaction need not be performed as a separate preliminary step, but can be triggered as a side effect of the dissolved metal-halide salt reacting with hexamethyl Dewar benzene.

Attempting a similar reaction with potassium tetrachloroplatinate results in the formation of a pentamethylcyclopentadiene complex, [(η4-Cp*H)PtCl2], indicating that the rhodium and iridium metal centres are necessary for the step in which the aromatic anion is formed.

Epoxidation One of the alkenes can be epoxidized using mCPBA, peroxybenzoic acid, or dimethyldioxirane (DMDO). By varying the amount of DMDO, either the mono- or diepoxide can be formed, with the oxygen atoms exo on the bicyclic carbon framework.

The epoxide products are stable when the oxidation is performed under neutral conditions, such as when using DMDO that has acetone as a byproduct. When Using a peracid (mCPBA or peroxybenzoic acid), the epoxy product quickly rearranges, catalyzed by the acid byproduct of the epoxidation.

Dication

In 1973, the dication of hexamethylbenzene, C6(CH3)2+6, was produced by Hepke Hogeveen and Peter Kwant. This can be done by dissolving the hexamethyl Dewar benzene monoepoxide in magic acid, which removes the oxygen as an anion. NMR had previously hinted at a pentagonal pyramidal structure in a related cation as had spectral data on the Hogeveen and Kwant dication. The pyramidal structure having an apex carbon bonding to six other carbon atoms was confirmed by X-ray crystallographic analysis of the hexafluoroantimonate salt published in 2016.

Computational organic chemist Steven Bachrach discussed the dication, noting that the weak bonds forming the upright edges of the pyramid, shown as dashed lines in the structure he drew, have a Wiberg bond order of about 0.54; it follows that the total bond order for the apical carbon is 5 × 0.54 + 1 = 3.7 < 4, and thus the species is not hypervalent, but it is hypercoordinate. From the perspective of organometallic chemistry, the species can be viewed as having a carbon(IV) centre (C4+) bound to an aromatic η5–pentamethylcyclopentadienyl anion (six-electron donor) and a methyl anion (two-electron donor), thereby satisfying the octet rule and being analogous to the gas-phase organozinc monomer [(η5–C5(CH3)5)Zn(CH3)], which has the same ligands bound to a zinc(II) centre (Zn2+) and satisfies the 18 electron rule on the metal. Thus, while unprecedented, and having attracted comment in Chemical & Engineering News, New Scientist, Science News, and ZME Science, the structure is consistent with the usual bonding rules of chemistry. Moritz Malischewski, who carried out the work with Konrad Seppelt, commented that one the motivations for undertaking the work was to illustrate "the possibility to astonish chemists about what can be possible."

References

Illustrations

Worked examples

Example 1 — a first encounter with Hexamethyl Dewar benzene

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

In research: Hexamethyl Dewar benzene appears in chemistry 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 Hexamethyl Dewar benzene 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: Hexamethyl Dewar benzene is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bicyclic compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Hexamethyl Dewar benzene 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Hexamethyl Dewar benzene” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Hexamethyl Dewar benzene in 20 minutes

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

Frequently asked questions

What is Hexamethyl Dewar benzene in simple terms?

Why does Hexamethyl Dewar benzene matter?

Because it connects several chemistry 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 Hexamethyl Dewar benzene?

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 Hexamethyl Dewar benzene.