With heterocycles containing five atoms, the unsaturated compounds are frequently more stable because of aromaticity.
Five-membered rings with one heteroatom:
|Nitrogen||Pyrrolidine (Azolidine is not used)||Pyrrole (Azole is not used)|
|Oxygen||Tetrahydrofuran(Oxolane is rare)||Furan (Oxole is not used)|
|Sulfur||Thiolane||Thiophene (Thiole is not used)|
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. Dithiolanes have two sulfur atoms.
|Heteroatom||Saturated||Unsaturated (and partially unsaturated)|
A large group of 5-membered ring compounds with three heteroatoms also exists. One example is dithiazoles that contain two sulfur and a nitrogen atom.
|3 × Nitrogen||Triazoles|
|2 × Nitrogen / 1 × oxygen||Furazan
|2 × Nitrogen / 1 × sulfur||Thiadiazole|
|1 × Nitrogen / 2 × sulfur||Dithiazole|
Five-member ring compounds with four heteroatoms:
|4 × Nitrogen||Tetrazole|
With 5-heteroatoms, the compound may be considered inorganic rather than heterocyclic. Pentazole is the all nitrogen heteroatom unsaturated compound.
Read more about this topic: Heterocyclic Compound
Famous quotes containing the word rings:
“You held my hand
and were instant to explain
the three rings of danger.”
—Anne Sexton (19281974)