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

Clinical Pharmacy PharmD - 2024/2025 Level 2 Pharmaceutical Organic Chemistry-3 (PC 305)
B- Polycylic rings or fused heterocyclic systems:

Rule 1:

When one heterocyclic ring is present, it is chosen as the parent component and the

name of the fused carbocyclic ring is attached as a prefix, e.g.

Rule 2: How to choose the parent ring?

Rules are applied according to the following order

a) When more than one heterocyclic ring is present, the parent ring must be first

determined, taking the following points in consideration:

The parent ring is:

1. Nitrogen-containing ring (nitrogen-containing rings are the most common).

Pyrrole is the parent component and not thiophene.

2. In case of absence of N, the ring having a heteroatom of higher priority is

the parent component. This priority is deduced from the previously given

table (O > S > etc.).

Furan is the parent component.