An ortho-fused compound in which at least one of the rings contains at least one heteroatom.
| Member | Definition | Role |
|---|
| cinnoline | An azaarene that is the 1,2-diaza analogue of naphthalene. The parent of the class of cinnolines. | cinnoline |
| hydralazine | The 1-hydrazino derivative of phthalazine; a direct-acting vasodilator that is used as an antihypertensive agent. | hydralazine |
| isoquinoline | An ortho-fused heteroarene that is a benzopyridine in which the N atom not directly attached to the benzene ring. | isoquinoline |
| phthalazine | An azaarene that is the 2,3-diaza analogue of naphthalene. The parent of the class of phthalazines. | phthalazine |
| pteridines | | pteridine |
| quinazolines | A mancude organic heterobicyclic parent that is naphthalene in which the carbon atoms at positions 1 and 3 have been replaced by nitrogen atoms. | quinazoline |
| quinoline | The simplest member of the quinoline class of compounds, comprising a benzene ring ortho fused to C-2 and C-3 of a pyridine ring. | quinoline |
| quinoxalines | A naphthyridine in which the nitrogens are at positions 1 and 4. | quinoxaline |