Document Details
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Document Type |
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Thesis |
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Document Title |
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Molecular Electronic Switch of 2-Hydroxypyridine/2-Pyridone Molecules: A quantum Mechanical/Molecular Dynamical Study جزيئات 2-هيدروكسي بيريدين/2-بيريدون كعاكسة جزيئية إلكترونية : دراسة بواسطة ميكانيكا الكم والديناميكا الجزيئية |
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Subject |
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Faculty of Sciences |
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Document Language |
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Arabic |
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Abstract |
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heterocyclic compound. It represents an important class of compounds, which have π- and n-electrons systems. It tautomerizes to form 2-Pyridone by a proton transfer between the nitrogen and oxygen atoms. The tautomerism between 2-Hydroxypyridine and 2-Pyridone has been confirmed by X-ray, IR, UV, and microwave spectroscopy, together with some theoretical studies. 2-Pyridones play important roles in bioactive systems and in current medicinal chemistry. The gas-phase thermal tautomerization reaction between 2-Hydroxypyridine (2-HP) and 2-Pyridone (2-PY) was investigated by applying 6-311++G** and aug-cc-PVDZ basis sets incorporated into some density functional theory (DFT) and coupled cluster with singles and doubles (CCSD) methods. The geometrical structures, dipole moments, HOMO-LUMO energy gaps, total hyperpolarizability, kinetics and thermodynamics functions were monitored against the effects of the corrections imposed on these functionals. The small experimental energy difference between the two tautomers of 3.23kJ/mol; was a real test of the accuracy of the applied levels of theory. M062X and CCSD methods predicted the preference of 2-HP over 2-PY by 5-9kJ/mol; while B3LYP functional favored 2-PY by 1-3kJ/mol. The CAM-B3LYP and ωB97XD functionals yielded mixed results depending on the basis set used. The source of preference of 2-HP is the minimal steric hindrance and electrostatic repulsion that subdued the huge hyperconjugation in 2-PY. A 1,3-proton shift intramolecular gas-phase tautomerization yielded a high average activation of 137.152kJ/mol; while the intermolecular mixed dimer interconversion gave an average barrier height of 30.844kJ/mol. These findings are boosted by a natural bond orbital (NBO) technique. The low total hyperpolarizabilities of both tautomers mark out their poor nonlinear optical (NLO) behavior. The enhancement of the total hyperpolarizability of 2-HP over that of 2-PY is interpreted by the bond length alternation.
Proton transfer reactions are important in many chemical and biological systems. Excited state proton transfer (ESPT) are specially important and have received considerable attention, because they play an important role in the proton relay occurring in enzymatic reactions, transport phenomena in biological membrane, and DNA mutations. Among many molecules undergoing this type of photoreactions are phenols which show a unique property, the so-called photoacidity. In the present communication, solvent (methanol and ammonia) assisted excited state proton transfer and photoacidity of 2-Hydroxypyridine (2-HP) are investigated at the DFT M06-2X / def2pvv level of theory. The decay of the excited states of 2-HP in the gas phase was examined by simulating the UV photoabsorption spectrum and nonadiabatic dynamics. The spectrum, composed of 10 excited states, was simulated with the nuclear ensemble approximation, sampling a Wigner distribution with 300 points. Dynamics simulations were done with the surface hopping method, started in separate spectral windows, of width ± 0.25 eV, to be compared to experimental UV spectral data. Three hundred trajectories were considered from each of these windows according to their excitation probabilities. The excited-state lifetime was determined. The main photochemical channel observed were analyzed and discussed. |
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Supervisor |
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Prof. Dr. Saadallah G. Aziz |
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Thesis Type |
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Master Thesis |
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Publishing Year |
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1438 AH
2017 AD |
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Co-Supervisor |
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Prof. Dr. Osman I. Abdelkarim |
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Added Date |
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Wednesday, March 29, 2017 |
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Researchers
| صفيه عارف حجازي | Hejazi, Safiyah Arif | Researcher | Master | |
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