5-Membered Rings
With heterocycles containing five atoms, the unsaturated compounds are frequently more stable because of aromaticity.
Five-membered rings with one heteroatom:
Heteroatom | Saturated | Unsaturated |
---|---|---|
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) |
Boron | Borolane | Borole |
Phosphorus | Phospholane | Phosphole |
Arsenic | Arsolane | Arsole |
Antimony | Stibolane | Stibole |
Bismuth | Bismolane | Bismole |
Silicon | Silolane | Silole |
Tin | Stannolane | Stannole |
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) |
---|---|---|
Nitrogen/nitrogen | Imidazolidine Pyrazolidine |
Imidazole (Imidazoline) Pyrazole (Pyrazoline) |
Nitrogen/oxygen | Oxazolidine Isoxazolidine |
Oxazole (Oxazoline) Isoxazole |
Nitrogen/sulfur | Thiazolidine Isothiazolidine |
Thiazole (Thiazoline) Isothiazole |
Oxygen/oxygen | Dioxolane | |
Sulfur/sulfur | Dithiolane |
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.
Heteroatom | Saturated | Unsaturated |
---|---|---|
3 × Nitrogen | Triazoles | |
2 × Nitrogen / 1 × oxygen | Furazan Oxadiazole |
|
2 × Nitrogen / 1 × sulfur | Thiadiazole | |
1 × Nitrogen / 2 × sulfur | Dithiazole |
Five-member ring compounds with four heteroatoms:
Heteroatom | Saturated | Unsaturated |
---|---|---|
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
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