chemistry

Nucleophilic abstraction

Nucleophilic abstraction 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 Nucleophilic abstraction rather than just read about it. In short: Nucleophilic abstraction is a type of an organometallic reaction which can be defined as a nucleophilic attack on a ligand which causes part or all of the original ligand to be removed from the metal along with the nucleophile. Alkyl abstraction While nucleophilic abstraction of an alkyl group is relatively uncommon, there are examples of this type of reaction.

Key takeaways

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

Reference excerpt

Nucleophilic abstraction is a type of an organometallic reaction which can be defined as a nucleophilic attack on a ligand which causes part or all of the original ligand to be removed from the metal along with the nucleophile.

Alkyl abstraction While nucleophilic abstraction of an alkyl group is relatively uncommon, there are examples of this type of reaction. In order for this reaction to be favorable, the metal must first be oxidized because reduced metals are often poor leaving groups. The oxidation of the metal causes the M-C bond to weaken, which allows for the nucleophilic abstraction to occur. G.M. Whitesides and D.J. Boschetto use the halogens Br2 and I2 as M-C cleaving agents in the following example of nucleophilic abstraction.

The product of this reaction is inverted with respect to the stereochemical center attached to the metal. There are several possibilities for the mechanism of this reaction which are shown in the following schematic.

In path a, the first step proceeds with the oxidative addition of the halogen to the metal complex. This step results in the oxidized metal center that is needed to weaken the M-C bond. The second step can proceed with either the nucleophilic attack of the halide ion on the α-carbon of the alkyl group or reductive elimination, both of which result in the inversion of stereochemistry. In path b, the metal is first oxidized without the addition of the halide. The second step occurs with a nucleophilic attack of the α-carbon which again results in the inversion of stereochemistry.

Carbonyl abstraction Trimethylamine N-oxide (Me3NO) can be used in the nucleophilic abstraction of carbonyl. There is an nucleophilic attack of Me3NO on the carbon of the carbonyl group which pushes electrons on the metal. The reaction then proceeds to kick out CO2 and NMe3.

An article from the Bulletin of Korean Chemical Society journal showed interesting results where one iridium complex undergoes carbonyl abstraction while a very similar iridium complex undergoes hydride extraction.

Hydrogen abstraction Nucleophilic abstraction can occur on a ligand of a metal if the conditions are right. For instance the following example shows the nucleophilic abstraction of H+ from an arene ligand attached to chromium. The electron withdrawing nature of the chromium allows for the reaction to occur as a facile reaction.

Methyl abstraction A Fischer carbene can undergo nucleophilic abstraction where a methyl group is removed. With the addition of a small abstracting agent, the abstracting agent would normally add to the carbene carbon. In this case however, the steric bulk of the abstracting agent that is added causes the abstraction of the methyl group. If the methyl group is replaced with ethyl, the reaction proceeds 70 times slower which is to be expected with a SN2 displacement mechanism.

Silylium abstraction A silylium ion is a silicon cation with only three bonds and a positive charge. The abstraction of the silylium ion is seen from the ruthenium complex shown below.

In the first step of this mechanism one of the acetonitrile groups is replaced by a silicon molecule where the bond between the silicon and the hydrogen is coordinating to the ruthenium. In the second step a ketone is added for the nucleophilic abstraction of the silylium ion and the hydrogen is left on the metal.

α-Acyl abstraction One example of nucleophilic abstraction of an α-acyl group is seen when MeOH is added to the following palladium complex. The mechanism follows a tetrahedral intermediate which results in the methyl ester and the reduced palladium complex shown.

The following year a similar mechanism was proposed where oxidative addition of an aryl halide followed by migratory CO insertion and is followed by nucleophilic abstraction of the α-acyl by MeOH. One of the advantages of this intermolecular nucleophilic abstraction is the production of linear acyl derivatives. The intramolecular attack of these linear acyl derivatives gives rise to cyclic compounds such as lactones or lactams.

Illustrations

Worked examples

Example 1 — a first encounter with Nucleophilic abstraction

Start with the simplest possible case. Write down what Nucleophilic abstraction 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 Nucleophilic abstraction 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 Nucleophilic abstraction 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 Nucleophilic abstraction

In research: Nucleophilic abstraction 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 Nucleophilic abstraction 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: Nucleophilic abstraction is common in secondary-school and first-year university syllabi. It links to neighbouring topics Inorganic chemistry, Organometallic chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Nucleophilic abstraction 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 Nucleophilic abstraction in 20 minutes

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

Frequently asked questions

What is Nucleophilic abstraction in simple terms?

Why does Nucleophilic abstraction 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 Nucleophilic abstraction?

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 Nucleophilic abstraction.