mathematics

Selenol

Selenol is a mathematics 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 Selenol rather than just read about it. In short: Selenols are organic compounds that contain the functional group with the connectivity C−Se−H. Selenols are sometimes also called selenomercaptans and selenothiols.

Key takeaways

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

Reference excerpt

Selenols are organic compounds that contain the functional group with the connectivity C−Se−H. Selenols are sometimes also called selenomercaptans and selenothiols. Selenols are one of the principal classes of organoselenium compounds. A well-known selenol is the amino acid selenocysteine.

Structure and properties Selenols are structurally similar to thiols, but the C−Se bond is about 8% longer at 196 pm. The C−Se−H angle approaches 90°. The bonding involves almost pure p-orbitals on Se, hence the near 90 angles. The Se−H bond energy is weaker than the S−H bond, consequently selenols are easily oxidized and serve as H-atom donors. The Se-H bond is weaker than the S−H bond as reflected in their respective bond dissociation energy (BDE). For C6H5Se−H, the BDE is 326 kJ/mol, while for C6H5S−H, the BDE is 368 kJ/mol. Selenols are about 1000 times stronger acids than thiols: the pKa of CH3SeH is 5.2 vs 8.3 for CH3SH. Deprotonation affords the selenolate anion, RSe−, most examples of which are highly nucleophilic and rapidly oxidized by air. The boiling points of selenols tend to be slightly greater than for thiols. This difference can be attributed to the increased importance of stronger van der Waals bonding for larger atoms. Volatile selenols have highly offensive odors.

Applications and occurrence

Selenols have few commercial applications, being limited by the toxicity of selenium as well as the sensitivity of the Se−H bond. Their conjugate bases, the selenolates, also have limited applications in organic synthesis.

Biochemical role Selenols are important in certain biological processes. Three enzymes found in mammals contain selenols at their active sites: glutathione peroxidase, iodothyronine deiodinase, and thioredoxin reductase. The selenols in these proteins are part of the essential amino acid selenocysteine. The selenols function as reducing agents to give selenenic acid derivative (RSe−OH), which in turn are re-reduced by thiol-containing enzymes. Methaneselenol (commonly named "methylselenol") (CH3SeH), which can be produced in vitro by incubating selenomethionine with a bacterial methionine gamma-lyase (METase) enzyme, by biological methylation of selenide ion or in vivo by reduction of methaneseleninic acid (CH3−Se(=O)−OH), has been invoked to explain the anticancer activity of certain organoselenium compounds. Precursors of methaneselenol are under active investigation in cancer prevention and therapy. In these studies, methaneselenol is found to be more biologically active than ethaneselenol (CH3CH2SeH) or 2-propaneselenol ((CH3)2CH(SeH)).

Preparation Selenols are usually prepared by the reaction of organolithium reagents or Grignard reagents with elemental Se. For example, benzeneselenol is generated by the reaction of phenylmagnesium bromide with selenium followed by acidification:

Another preparative route to selenols involves the alkylation of selenourea, followed by hydrolysis. Selenols are often generated by reduction of diselenides followed by protonation of the resulting selenolate:

2 RSe−SeR + 2 Li+[HB(CH2CH3)3]− → 2 RSe−Li+ + 2 B(CH2CH3)3 + H2 RSe−Li+ + HCl → RSeH + LiCl Organic reductants for this reaction include hypophosphorous acid. Dimethyl diselenide can be easily reduced to methaneselenol within cells.

Reactions Selenols are easily oxidized to diselenides, compounds containing an Se−Se bond. For example, treatment of benzeneselenol with bromine gives diphenyl diselenide.

2 C6H5SeH + Br2 → (C6H5Se)2 + 2 HBr In the presence of base, selenols are readily alkylated to give selenides. This relationship is illustrated by the methylation of methaneselenol to give dimethylselenide.

Safety Organoselenium compounds (or any selenium compound) are cumulative poisons despite the fact that trace amounts of Se are required for health.

Illustrations

Worked examples

Example 1 — a first encounter with Selenol

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

In research: Selenol appears in mathematics 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 Selenol 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: Selenol is common in secondary-school and first-year university syllabi. It links to neighbouring topics Functional groups, Selenols, so understanding it makes those chapters shorter.
In everyday life: Look for Selenol 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 Selenol in 20 minutes

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

Frequently asked questions

What is Selenol in simple terms?

Selenols are organic compounds that contain the functional group with the connectivity C−Se−H. Selenols are sometimes also called selenomercaptans and selenothiols.

Why does Selenol matter?

Because it connects several mathematics 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 Selenol?

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 Selenol.