Page 27 - Pharmaceutical Organic Chemmistry-3 (Theoritical book) 24-25

Clinical Pharmacy PharmD - 2024/2025 Level 2 Pharmaceutical Organic Chemistry-3 (PC 305)
7. The parent component is the ring with the higher priority heteroatoms.

1,3-Oxazole, not 1,3-thiazole, is the parent component.

8. The parent component is the ring in which, before fusion, the heteroatoms
carry the lowest locants (1,2- before 1,3- before 1,4....).

Pyridazine (1,2-) is the parent component rather than pyrimidine (1,3-

).

9. When the parent component has been chosen, its name is prefixed by the

name of the fused ring attached, e.g.

Benzoquinoline (not naphthopyridine)

Rule 3:

In order to indicate the positions of the ring junction (position of fusion):

• The bonds of the parent ring should have letters a, b, c, etc., starting with the a

letter for the side 1,2 and b for 2,3 .. etc.

• In case the parent is benzoheterocylic: a, b, c ….etc letters take the pathway of
heterocyclic ring first then the benzene ring

• In case the parent is heterocyclic ring: a, b, c, …. etc letters take the shortest

pathway towards the junction.