chemistry

Heterocyclic compound

Heterocyclic compound 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 Heterocyclic compound rather than just read about it. In short: A heterocyclic compound or ring structure is a hydrocarbon-based cyclic compound that contains at least one heteroatom as member(s) of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles.

Key takeaways

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

Reference excerpt

A heterocyclic compound or ring structure is a hydrocarbon-based cyclic compound that contains at least one heteroatom as member(s) of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles. Examples of heterocyclic compounds include all of the nucleic acids, the majority of drugs, most biomass (cellulose and related materials), and many natural and synthetic dyes. More than half of known compounds are heterocycles. 59% of US FDA-approved drugs contain nitrogen heterocycles.

Classification The study of organic heterocyclic chemistry focuses especially on organic unsaturated derivatives, and the preponderance of work and applications involves unstrained organic 5- and 6-membered rings. Included are pyridine, thiophene, pyrrole, and furan. Another large class of organic heterocycles refers to those fused to benzene rings. For example, the fused benzene derivatives of pyridine, thiophene, pyrrole, and furan are quinoline, benzothiophene, indole, and benzofuran, respectively. The fusion of two benzene rings gives rise to a third large family of organic compounds. Analogs of the previously mentioned heterocycles for this third family of compounds are acridine, dibenzothiophene, carbazole, and dibenzofuran, respectively. Heterocyclic organic compounds can be usefully classified based on their electronic structure. The saturated organic heterocycles behave like the acyclic derivatives. Thus, piperidine and tetrahydrofuran are conventional amines and ethers, with modified steric profiles. Therefore, the study of organic heterocyclic chemistry focuses on organic unsaturated rings.

Inorganic rings Some heterocycles contain no carbon. Examples are borazine (B3N3 ring), hexachlorophosphazene (P3N3 ring), and trithiazyl trichloride (S3N3 ring). In comparison with organic heterocycles, which have numerous commercial applications, inorganic ring systems are mainly of theoretical interest. IUPAC recommends the Hantzsch-Widman nomenclature for naming heterocyclic compounds.

Notes on lists "Heteroatoms" are atoms in the ring other than carbon atoms. Names in italics are retained by IUPAC and do not follow the Hantzsch-Widman nomenclature. Some of the names refer to classes of compounds rather than individual compounds. Also no attempt is made to list isomers.

3-membered rings Although subject to ring strain, 3-membered heterocyclic rings are well characterized.

4-membered rings

5-membered rings The 5-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are collectively called the azoles. Thiazoles and isothiazoles contain a sulfur and a nitrogen atom in the ring. Dithioles have two sulfur atoms. A large group of 5-membered ring compounds with three or more heteroatoms also exists. One example is the class of dithiazoles, which contain two sulfur atoms and one nitrogen atom.

6-membered rings The 6-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are collectively called the azines. Thiazines contain a sulfur and a nitrogen atom in the ring. Dithiines have two sulfur atoms.

Six-membered rings with five heteroatomsThe hypothetical chemical compound with five nitrogen heteroatoms would be pentazine. Six-membered rings with six heteroatomsThe hypothetical chemical compound with six nitrogen heteroatoms would be hexazine. Borazine is a six-membered ring with three nitrogen heteroatoms and three boron heteroatoms.

7-membered rings In a 7-membered ring, the heteroatom must be able to provide an empty π-orbital (e.g. boron) for "normal" aromatic stabilization to be available; otherwise, homoaromaticity may be possible.

8-membered rings

Borazocine is an eight-membered ring with four nitrogen heteroatoms and four boron heteroatoms.

9-membered rings

Images of rings with one heteroatom

Fused/condensed rings Heterocyclic rings systems that are formally derived by fusion with other rings, either carbocyclic or heterocyclic, have a variety of common and systematic names. For example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole provides indole or isoindole depending on the orientation. The pyridine derivative is quinoline or isoquinoline, and the class of analogues with two nitrogen atoms is known as the benzodiazines. For the azepine derivative, benzazepine is the preferred name. Likewise, the compounds with two benzene rings fused to the central heterocycle are carbazole, acridine, and dibenzoazepine. Heptazine is a tricyclic nitrogen-containing heterocyclic system derived by fusion of three triazine rings, and analog of the carbocycle phenalene.

History of heterocyclic chemistry The history of heterocyclic chemistry began in the 1800s, in step with the development of organic chemistry. Some noteworthy developments:

1818: Brugnatelli makes alloxan from uric acid. 1832: Dobereiner produces furfural (a furan) by treating starch with sulfuric acid. 1834: Runge obtains pyrrole ("fiery oil") by dry distillation of bones. 1906: Friedlander synthesizes indigo dye, allowing synthetic chemistry to displace a large agricultural industry. 1936: Treibs isolates chlorophyll derivatives from crude oil, explaining the biological origin of petroleum. 1951: Chargaff's rules are described, highlighting the role of heterocyclic compounds (purines and pyrimidines) in the genetic code.

Uses Heterocyclic compounds are pervasive in many areas of life sciences and technology. Many drugs are heterocyclic compounds. Among the modifications to the family of antitumor compounds, heterocyclic organic compounds have been extensively applied by many groups in order to modify the reactivity profile. Pyrrole, pyrimidine, indole, quinoline and purine are few classes of heterocycles which showed interesting cytotoxicity profiles, which can be highly beneficial when developing cancer drugs. Heterocyclic compounds play a central role in modern medicinal chemistry, with a large majority of newly approved drugs, containing at least one heterocyclic ring particularly nitrogen-containing systems. Their prevalence is attributed to their ability to modulate physicochemical properties such as solubility, lipophilicity, and binding affinity to biological targets.

Illustrations

Worked examples

Example 1 — a first encounter with Heterocyclic compound

Start with the simplest possible case. Write down what Heterocyclic compound 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 Heterocyclic compound 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 Heterocyclic compound 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 Heterocyclic compound

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

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

Frequently asked questions

What is Heterocyclic compound in simple terms?

Why does Heterocyclic compound 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 Heterocyclic compound?

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 Heterocyclic compound.