chemistry

Pentamethylarsenic

Pentamethylarsenic 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 Pentamethylarsenic rather than just read about it. In short: Pentamethylarsenic (or pentamethylarsorane) is an organometalllic compound containing five methyl groups bound to an arsenic atom with formula As(CH3)5. It is an example of a hypervalent compound.

Key takeaways

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

Reference excerpt

Pentamethylarsenic (or pentamethylarsorane) is an organometalllic compound containing five methyl groups bound to an arsenic atom with formula As(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramid.

History The first claim to make pentamethylarsenic was in 1862 in a reaction of tetramethylarsonium iodide with dimethylzinc by A. Cahours. For many years all the reproductions of this proved fruitless, so the production proved not to be genuine. It was actually discovered by Karl-Heinz Mitschke and Hubert Schmidbaur in 1973.

Production Trimethylarsine is chlorinated to trimethylarsine dichloride, which then reacts with methyl lithium to yield pentamethylarsenic.

As(CH3)3 + Cl2 → As(CH3)3Cl2 As(CH3)3Cl2 + 2LiCH3 → As(CH3)5 + 2LiCl Side products include As(CH3)4Cl and As(CH3)3=CH2. Pentamethylarsenic is not produced by biological organisms.

Properties Pentamethylarsenic smells the same as pentamethylantimony, but is otherwise unique. The bond lengths in the molecule are for the three equatorial As−C bonds 1.975 Å and the two axial As−C bonds 2.073 Å. The infrared spectrum of pentamethylarsenic shows strong bands at 582 and 358 cm−1 due to axial C-As vibration, and weaker bands at 265 and 297 cm−1 due to equatorial C-As vibration. Raman spectrum shows a strong feature at 519, 388, and 113 cm−1, and weak lines at 570 and 300 cm−1.

Reactions Pentamethylarsenic reacts slowly with weak acids. With water it forms tetramethylarsonium hydroxide As(CH3)4OH and trimethylarsenic oxide As(CH3)3O. With methanol, tetramethylmethoxyarsorane As(CH3)4OCH3 is produced. Hydrogen halides react resulting in the formation of tetramethylarsonium halide salts. When pentamethylarsenic is heated to 100° it decomposes forming trimethylarsine, methane, and ethylene. When trimethylindium reacts with pentamethylarsenic in benzene solution, a salt precipitates: tetramethylarsenic(V)tetramethylindate(III).

References

Illustrations

Worked examples

Example 1 — a first encounter with Pentamethylarsenic

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

In research: Pentamethylarsenic 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 Pentamethylarsenic 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: Pentamethylarsenic is common in secondary-school and first-year university syllabi. It links to neighbouring topics Arsenic(V) compounds, Hypervalent molecules, Organoarsenic compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Pentamethylarsenic 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 Pentamethylarsenic in 20 minutes

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

Frequently asked questions

What is Pentamethylarsenic in simple terms?

Pentamethylarsenic (or pentamethylarsorane) is an organometalllic compound containing five methyl groups bound to an arsenic atom with formula As(CH3)5. It is an example of a hypervalent compound.

Why does Pentamethylarsenic 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 Pentamethylarsenic?

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 Pentamethylarsenic.