chemistry

Selenopyrylium

Selenopyrylium 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 Selenopyrylium rather than just read about it. In short: Selenopyrylium is an aromatic heterocyclic compound consisting of a six-membered ring with five carbon atoms and a positively charged selenium atom. Naming and numbering Formerly it was named selenapyrylium.

Key takeaways

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

Reference excerpt

Selenopyrylium is an aromatic heterocyclic compound consisting of a six-membered ring with five carbon atoms and a positively charged selenium atom.

Naming and numbering Formerly it was named selenapyrylium. However, this is misleading as "selena" indicates that selenium substitutes for a carbon atom, but actually selenium is substituted for the oxygen atom in pyrylium. In the Hantzsch-Widman system of nomenclature, it is called seleninium. This is the name used by Chemical Abstracts. Replacement nomenclature would call this selenoniabenzene. Numbering in selenopyrylium starts with 1 on the selenium atom and counts up to 6 on the carbon atoms. The positions adjacent to the chalcogen, numbered 2 and 6 can also be called α, the next two positions 3 and 5 can be termed "β" and the opposite carbon at position 4 can be called "γ".

Occurrence Because selenopyrylium is a positively charged ion, it takes the solid form as a salt with non-nucleophillic anions such as perchlorate, tetrafluoroborate, fluorosulfate, and hexafluorophosphate.

Formation Selenopyrylium and derivatives can be made from 1,5-diketones (such as glutaraldehyde) and hydrogen selenide, along with hydrogen chloride (HCl) as a catalyst using acetic acid as a solvent. A side product is 2,6-bis-(hydroseleno)selenacyclohexane. When 5-chloro-2,4-pentadienenitrile derivatives react with sodium hydroselenide, or sodium selenite, and are then treated with perchloric acid, a 2-amino-selenopyrilium perchlorate salt results.

Properties The positive charge is not confined to the selenium atom, but distributes on the ring in several resonance structures, so that the α and γ positions have some positive charge. A nucleophillic attack targets these carbon atoms. Selenopyrylium has two prominent absorption bands in the ultraviolet spectrum, band I is at 3000 Å, and band II is at 2670 Å. Band I, also known as 1Lb is from the 1B1←1A1 transition. The wavelength is longer and the band is much stronger than that of benzene. This is a bathochromic shift. The wavelength is longer than in thiopyrylium and pyrylium, but the intensity is weaker, due to selenium being less electronegative. Band II, also called 1La, is stronger and longer than that of benzene, thiopyrylium and pyrylium. Band II is polarized in the direction of Se-γ axis. The nuclear magnetic resonance spectrum shows a 10.98 ppm shift for H2 and 6, 8.77 for H3 and H5 and 9.03 for H4 (BF4− salt dissolved in CD3CN). Compared to other pyryliums H2,6 is more than that of oxygen or sulfur, H3,5 is between that of oxygen and sulfur, and H4 is very similar to thiopyrylium, but is slightly lower. NMR for 13C has the same trends as for the attached hydrogens. Solvents include trifluoroacetic acid, methanol, dichloromethane, chloroform, and acetonitrile.

Derivatives Many derivatives of selenopyrylium are known with side chains attached to carbons 2, 3, or 6. Examples include 4-(p-dimethylaminophenyl)selenopyridinium, 2,6-diphenylselenopyridinium, 4-methyl-2,6-diphenylselenopyrylium, 2,4,6-triphenylselenopyrylium, 2,6-diphenyl-4-(p-dimethylaminophenyl)selenopyrylium, and 2,6-di-tert-butylselenopyrylium.

Related When the ring is fused with other aromatic rings, larger aromatic structures such as selenochromenylium, selenoflavylium, and selenoxanthylium result.

See also 6-membered aromatic rings with one carbon replaced by another group: borabenzene, silabenzene, germabenzene, stannabenzene, pyridine, phosphorine, arsabenzene, stibabenzene, bismabenzene, pyrylium, thiopyrylium, selenopyrylium, telluropyrylium

References

Illustrations

Worked examples

Example 1 — a first encounter with Selenopyrylium

Start with the simplest possible case. Write down what Selenopyrylium 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 Selenopyrylium 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 Selenopyrylium 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 Selenopyrylium

In research: Selenopyrylium 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 Selenopyrylium 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: Selenopyrylium is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aromatic compounds, Cations, Heterocyclic compounds with 1 ring, so understanding it makes those chapters shorter.
In everyday life: Look for Selenopyrylium 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 Selenopyrylium in 20 minutes

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

Frequently asked questions

What is Selenopyrylium in simple terms?

Selenopyrylium is an aromatic heterocyclic compound consisting of a six-membered ring with five carbon atoms and a positively charged selenium atom. Naming and numbering Formerly it was named selenapyrylium.

Why does Selenopyrylium 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 Selenopyrylium?

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 Selenopyrylium.