chemistry

Molecular Borromean ring

Molecular Borromean ring 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 Molecular Borromean ring rather than just read about it. In short: In chemistry, molecular Borromean rings are an example of a mechanically-interlocked molecular architecture in which three macrocycles are interlocked in such a way that breaking any macrocycle allows the others to dissociate. They are the smallest examples of Borromean rings.

Key takeaways

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

Reference excerpt

In chemistry, molecular Borromean rings are an example of a mechanically-interlocked molecular architecture in which three macrocycles are interlocked in such a way that breaking any macrocycle allows the others to dissociate. They are the smallest examples of Borromean rings. The synthesis of molecular Borromean rings was reported in 2004 by the group of J. Fraser Stoddart. The so-called Borromeate is made up of three interpenetrated macrocycles formed through templated self assembly as complexes of zinc.

The synthesis of the macrocyclic systems involves self-assembles of two organic building blocks: 2,6-diformylpyridine (an aromatic compound with two aldehyde groups positioned ortho to the nitrogen atom of the pyridine ring) and a symmetric diamine containing a meta-substituted 2,2'-bipyridine group. Zinc acetate is added as the template for the reaction, resulting in one zinc cation in each of the six pentacoordinate complexation sites. Trifluoroacetic acid (TFA) is added to catalyse the imine bond-forming reactions. The preparation of the tri-ring Borromeate involves a total of 18 precursor molecules and is only possible because the building blocks self-assemble through 12 aromatic pi-pi interactions and 30 zinc to nitrogen dative bonds. Because of these interactions, the Borromeate is thermodynamically the most stable reaction product out of potentially many others. As a consequence of all the reactions taking place being equilibria, the Borromeate is the predominant reaction product.

Reduction with sodium borohydride in ethanol affords the neutral Borromeand. With the zinc removed, the three macrocycles are no longer chemically bonded but remain "mechanically entangled in such a way that that if only one of the rings is removed the other two can part company." The Borromeand is thus a true Borromean system as cleavage of just one imine bond (to an amine and an acetal) in this structure breaks the mechanical bond between the three constituent macrocycles, releasing the other two individual rings. A borromeand differs from a [3]catenane in that none of its three macrocycles is concatenated with another other; if one bond in a [3]catenane is broken and a cycle removed, a [2]catenane can remain.

Organic synthesis of this seemingly complex compound is in reality fairly simple; for this reason, the Stoddart group has suggested it as a gram-scale laboratory activity for undergraduate organic chemistry courses.

See also Dynamic covalent chemistry Molecular knot Topology (chemistry)

References

External links

Freemantle, Michael (May 31, 2004). "Three rings in an inseparable union". Chemical & Engineering News. 82 (22): 5. doi:10.1021/cen-v082n022.p005. Borromean chemistry overview website

Illustrations

Molecular Borromean ring: Schematic of a molecular Borromean ring. — Schematic of a molecular Borromean ring.

Worked examples

Example 1 — a first encounter with Molecular Borromean ring

Start with the simplest possible case. Write down what Molecular Borromean ring 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 Molecular Borromean ring 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 Molecular Borromean ring 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 Molecular Borromean ring

In research: Molecular Borromean ring 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 Molecular Borromean ring 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: Molecular Borromean ring is common in secondary-school and first-year university syllabi. It links to neighbouring topics Molecular topology, Supramolecular chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Molecular Borromean ring 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 Molecular Borromean ring in 20 minutes

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

Frequently asked questions

What is Molecular Borromean ring in simple terms?

Why does Molecular Borromean ring 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 Molecular Borromean ring?

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 Molecular Borromean ring.