Page 50 - Pharmaceutical Organic Chemmistry-3 (Theoritical book) 24-25

Clinical Pharmacy PharmD - 2024/2025 Level 2 Pharmaceutical Organic Chemistry-3 (PC 305)
II- FIVE-MEMBERED HETEROCYCLES with

TWO or MORE HETEROATOMS

1. Two heteroatoms may be either:

a. Two nitrogen atoms (pyrazole and imidazole).

b. Two different heteroatoms, (oxazole N, O) and (thiazole N, S).

(The two heteroatoms may be situated in the 1,2- or 1,3-positions leading to 1,2- and

1,3-azoles, respectively).

2. More than two heteroatoms

(triazole, 3N), (tetrazole, 4N), (oxadiazole, 2N, O) and (thiadiazole, 2N, S).

All these ring systems belong to the -excessive heteroaromatics. Each ring has a

delocalized sextet of -electrons (4n+2).