Within: aromatic ring.

A compound has heteroaromatic ring when it has any of the groups below. A parent group is never matched itself, and its count of a compound is the number of occurrences of all of them together.

Parent groups under it: azine (6-ring), azole (5-ring), heteroaromatic lactam (pyridinone, pyrimidinone).

Groups directly under it

Through the parent groups above, also: pyridine, pyrimidine, pyridinone (2-/4-pyridone), pyrimidinone (uracil/cytosine type), pyrazine, pyridazine, 1,3,5-triazine, 1,2,3-/1,2,4-triazine, tetrazine, pyrrole, indole, imidazole, pyrazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole, oxazole, isoxazole, thiazole, isothiazole, oxadiazole, thiadiazole.

In the ATB

• 41,469 annotated compounds have it;
• 180 of them have experimental reference data;
• 2,517 are monofunctional: this is their only group, once (rings count as groups, so a phenol is not).

The annotated compounds are those with experimental reference data plus small, neutral organic compounds (up to 12 heavy atoms), not every ATB molecule. Through the API: GET /api/v1/molecules?functional_group=heteroaromatic.

Annotation scheme 2.