chemistry

Thorpe–Ingold effect

Thorpe–Ingold effect 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 Thorpe–Ingold effect rather than just read about it. In short: The Thorpe–Ingold effect, gem-dimethyl effect, or angle compression is an effect observed in chemistry where increasing steric hindrance favours ring closure and intramolecular reactions. The effect was first reported by Beesley, Thorpe, and Ingold in 1915 as part of a study of cyclization reactions.

Key takeaways

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

Reference excerpt

The Thorpe–Ingold effect, gem-dimethyl effect, or angle compression is an effect observed in chemistry where increasing steric hindrance favours ring closure and intramolecular reactions. The effect was first reported by Beesley, Thorpe, and Ingold in 1915 as part of a study of cyclization reactions. It has since been generalized to many areas of chemistry. The comparative rates of lactone formation (lactonization) of various 2-hydroxybenzenepropionic acids illustrate the effect. The placement of an increasing number of methyl groups accelerates the cyclization process.

One application of this effect is addition of a quaternary carbon (e.g., a gem-dimethyl group) in an alkyl chain to increase the reaction rate and/or equilibrium constant of cyclization reactions. An example of this is an olefin metathesis reaction: In the field of peptide foldamers, amino acid residues containing quaternary carbons such as 2-aminoisobutyric acid are used to promote formation of certain types of helices.

One proposed explanation for this effect is that the increased size of the substituents increases the angle between them. As a result, the angle between the other two substituents decreases. By moving them closer together, reactions between them are accelerated. It is thus a kinetic effect.

The effect also has some thermodynamic contribution as the in silico strain energy decreases on going from cyclobutane to 1-methylcyclobutane and 1,1-dimethylcyclobutane by a value between 8 kcal/mole and 1.5 kcal/mole. A noteworthy example of the Thorpe-Ingold effect in supramolecular catalysis is given by diphenylmethane derivatives provided with guanidinium groups. These compounds are active in the cleavage of the RNA model compound HPNP. Substitution of the methylene group of the parent diphenylmethane spacer with cyclohexylidene and adamantylidene moieties enhances catalytic efficiency, with gem dialkyl effect accelerations of 4.5 and 9.1, respectively.

See also Chelate effect Flippin–Lodge angle Baldwin's rules

References

Illustrations

Worked examples

Example 1 — a first encounter with Thorpe–Ingold effect

Start with the simplest possible case. Write down what Thorpe–Ingold effect 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 Thorpe–Ingold effect 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 Thorpe–Ingold effect 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 Thorpe–Ingold effect

In research: Thorpe–Ingold effect 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 Thorpe–Ingold effect 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: Thorpe–Ingold effect is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical kinetics, Physical organic chemistry, Stereochemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Thorpe–Ingold effect 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 Thorpe–Ingold effect in 20 minutes

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

Frequently asked questions

What is Thorpe–Ingold effect in simple terms?

Why does Thorpe–Ingold effect 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 Thorpe–Ingold effect?

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 Thorpe–Ingold effect.