Investigation of the Stability of Oxadiasole and Their Analogs Using Quantum Mechanics Computation

This study aimed at investigating factors affecting the stability as well as structural properties of different Oxadiasole and Thiadiasole isomers based on theoretical level B3LYP/6-311+G**, Nuclear Magnetic Resonance (NMR), and Nucleus-independent Chemical Shift (NICS). Qualitative relationships between relative stabilities of 1,2,3-Oxadiazole, 1,2,4-Oxadiazole, 1,2,5-Oxadiazole and 1,3,4-Oxadiazole were obtained. Aromatic stabilization energy (ASE), aromatic ring current (NICS), HUMO-LUMO gaps, electro-negativity (X), hardness (η), softness (S), electro-philicity (ω) and structural parameters were also calculated in the same theoretical level. The results show that 1,3,4-Oxadiazole is more stable than 1,2,3-Oxadiazole, 1,2,4-Oxadiazole and 1,2,5-Oxadiazole. Unlike the trends observed in Oxadiazoles, 1,2,5-Thiadiazole isomer is more stable than other corresponding Isomers.