Back to: Organic Chemistry 200 Level
Welcome to class!
Hello bright mind! In our last lesson, we saw how heterocyclic compounds are like rings with “special guests” — atoms other than carbon that change the ring’s personality. Today, we’ll look deeper at some important individual heterocycles, their structures, properties, and why they’re so valuable in chemistry and everyday life.
Heterocyclic Compounds II
Focus on Common Five-Membered Aromatic Heterocycles
Furan (C₄H₄O)
Structure: A five-membered aromatic ring with one oxygen atom.
Source: Can be made from dehydration of certain sugars.
Properties: Colourless liquid with a pleasant smell, but quite reactive.
Uses: In making pharmaceuticals and as a starting material for resins.
Pyrrole (C₄H₅N)
Structure: Five-membered ring with one nitrogen atom.
Source: Found in haem, the red pigment in blood.
Properties: Weakly basic, aromatic, and participates in many substitution reactions.
Uses: In making dyes, drugs, and conducting polymers.
Thiophene (C₄H₄S)
Structure: Five-membered aromatic ring with one sulphur atom.
Source: Often present in crude oil.
Properties: Aromatic like benzene, relatively stable, and used in making special materials.
Uses: In manufacturing dyes, drugs, and agrochemicals.
Focus on Common Six-Membered Aromatic Heterocycles
Pyridine (C₅H₅N)
Structure: Six-membered ring with one nitrogen atom.
Properties: Colourless liquid with an unpleasant smell; basic and miscible with water.
Uses: As a solvent, and in making vitamins, herbicides, and drugs.
Quinoline (C₉H₇N) and Isoquinoline (C₉H₇N)
Structure: Fused ring systems containing nitrogen.
Uses: In antimalarial drugs (e.g., quinine), dyes, and pesticides.
Reactivity of Aromatic Heterocycles
Electrophilic Substitution: Furan, pyrrole, and thiophene are more reactive than benzene because the heteroatom donates electrons to the ring.
Nucleophilic Substitution: Pyridine is more reactive towards nucleophiles because the nitrogen atom withdraws electrons from the ring, activating certain positions.
Importance in Real Life
Medicine: Many drugs like anti-inflammatory agents, antibiotics, and antimalarials have heterocyclic rings.
Agriculture: Used in making fungicides and insecticides.
Materials Science: Found in conductive materials and dyes.
Summary
- Furan, pyrrole, thiophene, and pyridine are key aromatic heterocycles.
- Their reactivity depends on the nature of the heteroatom.
- They are vital in medicine, agriculture, and materials development.
Evaluation
- Which heterocycle is found in haem?
- Why is furan more reactive towards electrophiles than benzene?
- Name one six-membered nitrogen-containing heterocycle.
- Give one use of thiophene in industry.
Fantastic job! You’re now building a strong understanding of the chemical “architectures” that power life, technology, and health. With Afrilearn, you’re not just learning chemistry— you’re gaining tools to change the world.