| Member | Definition | Role |
|---|
| furan | A monocyclic heteroarene with a structure consisting of a 5-membered ring containing four carbons and one oxygen, with formula C4H4O. It is a toxic, flammable, low-boiling (31degreeC) colourless liquid. | furan |
| isoxazoles | A monocyclic heteroarene with a structure consisting of a 5-membered ring containing three carbon atoms and an oxygen and nitrogen atom adjacent to each other. It is the parent of the class of isoxazoles. | isoxazole |
| oxazoles | A five-membered monocyclic heteroarene that is an analogue of cyclopentadiene with O in place of CH2 at position 1 and N in place of CH at position 3. | 1,3-oxazole |
| oxirene | | oxirene |
| pyridine | An azaarene comprising a benzene core in which one -CH group is replaced by a nitrogen atom. It is the parent compound of the class pyridines. | pyridine |
| thiazoles | | thiazole |
| thiophenes | A monocyclic heteroarene that is furan in which the oxygen atom is replaced by a sulfur. | thiophene |