Density Functional Studies on Reactivity of Thiazole and Some of its Derivatives in the Gas Phase دراسات في النشاط الكيميائى للثيازول و بعضٍ من مشتقاته في الحالة الغازية بواسطة نظرية الكثافة الوظيفية

المقادمة, أحمد and صافي, زكي and عنابة, علاء (2020) Density Functional Studies on Reactivity of Thiazole and Some of its Derivatives in the Gas Phase دراسات في النشاط الكيميائى للثيازول و بعضٍ من مشتقاته في الحالة الغازية بواسطة نظرية الكثافة الوظيفية. Al-Aqsa University Journal (Natural Sciences Series), 22 (1). pp. 74-113. ISSN 2070-3155 (Print), ISSN 2521-893X (Online)

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Abstract

The preference of B3LYP functional over eleven different hybrid functional in case of thiazole in the presence of 6-311++G(d,p) and aug-cc-pV(Q+d)Z basis sets was initially established through statistical evaluation of the estimated geometrical parameters with the observed ones. Thiazole and its derivatives were fully optimized at DFT(B3LYP) with the aforementioned basis sets and ground state nature of each was confirmed through frequency calculations. Proton affinity, gas-phase basicity, and chemical reactivity descriptors; frontier orbital, energy gap, chemical hardness, softness, electronegativity, electrophilicity and nucleophilicity were estimated at B3LYP/6-311++G (3df,2p)//B3LYP/6-311++G(d,p). Aromaticity characteristics were confirmed using Harmonic Oscillator Model of Aromaticity (HOMA), Harmonic Oscillator Model of Heterocyclic Electron Delocalization (HOMHED) and Nucleus Independent Chemical Shift (NICS). NICS calculations reflected that the aromaticity of thiazole is higher than any of its derivatives, while HOMA and HOMHED calculations showed that the aromatic characteristic superiority is associated with 2- nitrothiazole. Results indicated that thiazole and its derivatives behave as nitrogen bases with moderate strength. Proton affinity and gas phase basicity calculations were confirmed by Global reactivity calculations. Energy gap and chemical hardness reflected a remarkable thiazole chemical stability. Substituent effect on structural properties, aromaticity, PAs, GBs and global reactivity descriptors has been established. Calculations showed, almostly, the order of reactivity based on the substituent group is Ph >NH2  NO2 and that 2-phenylthiazole showed the best corrosion inhibition efficiency

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