1,3,4-Oxadiazole is a five-membered, conjugated, planar, stable heteroaromatic, comprised of two adjacent nitrogen atoms at the 3,4-positions with one oxygen atom and two vicinal carbon atoms. Each nitrogen atom in the ring is one carbon apart from the oxygen heteroatom. The 1,3,4-oxadiazole ring is electron deficient due to the presence of two pyridine-like nitrogen atoms in the ring and as a result its chemical properties are unlike those of furan as evidenced from the downfield chemical shift of C2(5)H at δ 8.73 ppm (CDCl3) of the parent 1,3,4-oxadiazole. The presence of two electronegative nitrogen atoms deactivates the ring, making electrophilic substitution difficult in the ring at the C2- and C5-positions. From a medicinal chemistry point of view, it is a very important molecule because it is a surrogate of carboxylic acids, esters, and carboxamides and displays a wide spectrum of pharmacological activities.
